WO2009049289A1

WO2009049289A1 - Temperature control in froth flotation processes

Info

Publication number: WO2009049289A1
Application number: PCT/US2008/079715
Authority: WO
Inventors: Stephen C. Paspek; Joseph E. Bork; Alan Schroeder; Christopher Kulbago
Original assignee: BROADVIEW GROUP LLC
Current assignee: BROADVIEW GROUP LLC
Priority date: 2007-10-11
Filing date: 2008-10-13
Publication date: 2009-04-16
Anticipated expiration: 2010-04-11

Abstract

A process is described for the separation of a mixture of solid particles of similar specific gravity into at least two fractions comprises introducing the particles in an aqueous medium, adding air to form bubbles, and generating two or more product streams, one of which floats and the other which sinks. The yield and purity of each of the product streams is a strong function of the temperature at which the separation occurs. High temperatures favor a greater yield of hydrophobic particles in the floating product stream and an increased level of purity.

Description

TEMPERATURE CONTROL IN FROTH FLOTATION PROCESSES

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority upon US provisional application serial No. 60/979,253 filed October 11 , 2007.

FIELD OF THE INVENTION

[0002] The present invention relates to reclaiming one or more solid particulate components, such as ground or comminuted plastics, from a mixture of components in which at least some of the components have similar densities as the particulates of interest, by froth flotation. Such particles are not amenable to separation by traditional "float-sink" technology. More specifically, the present invention relates to the use of temperature control in a froth flotation system or process as a strategy for improving the yield and purity of product streams.

BACKGROUND OF THE INVENTION

[0003] Various processes are known for separating ground or comminuted materials, such as in the fields of recycling and material reclamation. A frequently used process operation is a float-sink operation in which a mixture or feed of various materials is introduced into a liquid medium having a specific density. Materials having a density greater than that of the medium sink, and materials having a density less than that of the medium float. This process is useful for separating materials in a wide range of material mixtures.

[0004] However, float-sink operations are generally ineffective for separating materials having the same or similar densities. And so, it is necessary to utilize a different separation technique. Froth flotation processes have been used to separate materials having the same or similar densities. Froth flotation separation processes rely upon differences in the "wettability" of materials, and specifically, their relative degrees of hydrophilicity or hydrophobicity. Froth flotation likely originated in the mining and ore processing industry, as exemplified by US Patents 1 ,911 ,865; 2,105,294; 2,188,932; and 2,588,443. Although apparently useful for separation and/or concentration of ores and minerals, the processes described in those patents are typically performed using liquid mill concentrates containing various ores, and adding a flotation agent such as fish oil, crude oil, kerosene, or the like. [0005] Froth flotation processes have also been used to separate plastic materials having the same or similar densities. For example, US Patents 3,925,200; 3,926,790; and 3,926,791 to Izumi et al. describe separating a mixture of plastics by froth flotation using an alkali metal or alkaline earth metal salt or lignin sulfonic acid and/or a hydrophilic organic colloid as a conditioning agent. The conditioning agent is said to cause a difference in the wetting characteristics between surfaces of the various plastics. US Patent 3,985,650 to Saitoh et al. describes separating a plastic from a mixture of materials using froth flotation and certain wetting agents and flotation agents. US Patent 4,167,477 to Valdez et al. describes separating mixtures of plastic materials by froth flotation using sodium silicate as a wetting agent and various fatty amines or salts thereof as cationic promoters. US Patent 4,132,633 to Saitoh et al. is directed to separating particular mixtures of plastics using certain wetting agents via froth flotation. US Patent 5,234,110 to Kobler describes separating a mixture of polyvinyl chloride chips from polyethylene terephthalate chips in a froth flotation process by treating the chips with a surface conditioning agent. US Patent 5,248,041 to Deiringer et al. is directed to a froth flotation process in which certain plastics can be recovered from a mixture of plastics. Prior to flotation, the mixture of plastics is treated in an aqueous alkaline solution. US Patent 5,377,844 to

Hwang separates plastics that are said to have hydrophobic surface characteristics, by conditioning the plastic materials with a heteropolar surfactant.

[0006] Although satisfactory in many respects, each of these processes for separating plastics by froth flotation requires a wetting or conditioning agent, or a pretreatment operation in which the plastic materials are contacted with a particular agent or solution. Requiring one or more of these operations in a froth flotation operation increases process complexity, time requirements, and cost in an overall separation strategy, and so is generally undesirable.

[0007] Accordingly, it would be beneficial to provide a froth flotation process in which materials having the same or similar densities could be separated, without the requirement of a wetting or conditioning agent.

[0008] Furthermore, it would be desirable to provide a froth flotation process in which materials having the same or similar densities could be separated, without the requirement of a pretreatment operation for modifying the surface characteristics of the materials to be separated.

[0009] Moreover, it would be desirable to provide a froth flotation process in which plastic materials having the same or similar densities could be separated, without the requirement of a wetting agent, a conditioning agent, or a pretreatment operation for modifying the surface characteristics of the plastic materials to be separated. SUMMARY OF THE INVENTION

[0010] The difficulties and drawbacks associated with previous methods and systems are overcome in the present invention providing various strategies for separating solid materials having the same or similar densities, and particularly for separating plastics via a froth flotation operation.

[0011] In one aspect, the present invention provides a froth flotation process for forming from a particulate feed, a first output including hydrophobic particulates of a first material and a second output including less hydrophobic particles of a second material. The first material and the second material have the same or similar densities. The process comprises adding the particulate feed to an aqueous aerated medium. The process also comprises heating the aqueous medium whereby the yield of the hydrophobic particles of the first material in the first output is increased. [0012] In another aspect, the present invention provides a method for increasing recovery of hydrophobic materials in a first output of a froth flotation system. The froth flotation system comprises a vessel adapted to retain an aqueous aerated medium and produce the first output and a second output. The first output includes a greater proportion of hydrophobic materials than the second output. The method comprises introducing a particulate feed to an aqueous medium in a froth flotation system. The particulate feed includes at least two materials differing in hydrophobicity. The method also comprises heating the aqueous medium whereby the proportion of hydrophobic materials in the first output is increased. [0013] In another aspect, the present invention provides a method for increasing recovery of hydrophilic materials in a second output of a froth flotation system. The froth flotation system comprises a vessel adapted to retain an aqueous aerated medium and produce a first output and the second output. The second output includes a greater proportion of hydrophilic materials than the first output. The method comprises introducing a particulate feed to an aqueous medium in a froth flotation system. The particulate feed includes at least two materials differing in hydrophilicity. The method also comprises heating the aqueous medium whereby the proportion of hydrophilic materials in the second output is increased. [0014] In yet another aspect, the present invention provides a method for reducing the concentration of contaminants in a first output of a froth flotation system. The froth flotation system comprises a vessel adapted to retain an aqueous aerated medium and produce the first output and a second output. The first output includes a greater proportion of hydrophobic materials than the second output. The method comprises introducing a comminuted feed to an aqueous medium in a froth flotation system, the feed including at least two materials differing in hydrophobicity. The method also comprises heating the aqueous medium whereby the concentration of contaminants in the first output is decreased.

[0015] In a further aspect, the present invention provides a process for separating a first plastic from a particulate mixture including the first plastic and at least one other plastic having the same or similar density. The process is free of any preconditioning or pretreatment operation in which the first plastic and/or other plastics are contacted with a conditioning agent. The process comprises providing a froth flotation system comprising a vessel and an aqueous aerated medium disposed in the vessel. The process further comprises adding the particulate mixture to the aqueous aerated medium whereby a first output including a majority of the first plastic is produced. The temperature of the liquid medium is at least 90⁰F. [0016] As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic illustration of a froth flotation unit utilized in association with the present invention.

[0018] Figure 2 is a schematic flow chart illustrating a system of multiple froth flotation units utilized in association with the present invention. [0019] Figure 3 is a graph of data presented in Table 1 illustrating the relationship between increasing concentration of a desired component in a float product as temperature of a liquid medium increases.

[0020] Figure 4 is a graph of data presented in Table 1 illustrating the relationship between decreasing concentration of a contaminant component in a float product as temperature of a liquid medium increases.

[0021] Figure 5 is a graph of data presented in Table 1 illustrating the relationship between increasing concentration of a desired component in a float product as temperature of a liquid medium increases.

[0022] Figure 6 is a graph of data presented in Table 1 illustrating the relationship between decreasing concentration of a contaminant component in a float product as temperature of a liquid medium increases.

[0023] Figure 7 is a graph of data presented in Table 1 illustrating the relationship between increasing concentration of a desired component in a float product as temperature of a liquid medium increases. [0024] Figure 8 is a graph of data presented in Table 1 illustrating the relationship between decreasing concentration of a contaminant component in a float product as temperature of a liquid medium increases.

DETAILED DESCRIPTION OF THE EMBODIMENTS [0025] Mixtures of particles of different materials have limited value due to substantial differences in physical properties of the various materials. The value of such mixtures can be improved by separating them into two or more portions or streams, each containing particles having similar physical properties. [0026] In the case of recycled plastics, for example, one may encounter a stream of particles consisting of flexible polyvinyl chloride (PVC) admixed with rubber, silicone, filled polyethylene, filled polypropylene, etc. from which it is desirable to extract a stream rich in flexible PVC particles. The term "filled" refers to the addition of non-polymeric substances such as various minerals, flame retardants, densifiers, calcium carbonate, silica, etc. to a polymeric compound for a variety of reasons. Since all of the particles have approximately the same density, e.g. in the range of 1.2 to 1.5 g/cm³, it is not possible to efficiently separate these particles by a float-sink operation that differentiates particles based on density. [0027] Throughout the description of the present invention and its various preferred aspects, reference is made to separating or recovering at least one plastic from other plastics and potentially other solids having the same or similar density or specific gravity as that of the plastic of interest. The phrase "the same or similar density" (or specific gravity) refers to densities or ranges of densities of the plastic(s) of interest and other materials in the mixture which are from about ±30% of each other, or as is more typical with density ranges, overlap each other. [0028] Certain mixtures of particles with the same or similar densities such as plastics have been separated by froth flotation. Froth flotation is a well known process that uses air bubbles to cause the more hydrophobic particles in a mixture to float to the surface of an aqueous slurry while the more hydrophilic particles tend to sink. Various chemicals can be added to improve bubble stability, change surface tension, and alter the surface properties of particles. Froth flotation causes particles to separate based on the relative hydrophobicity of a particle's surface, with the more hydrophobic particles adhering to the bubbles and reporting to the surface of the liquid, while the less hydrophobic particles (i.e. more hydrophilic particles) tend to "wet", and sink in the process fluid.

[0029] Froth flotation can be used to effect a separation based on the relative hydrophobicity of the particles. Since PVC is the most hydrophobic material in the previously noted particulate mixture, that material tends to more selectively report to the surface of the slurry. The selectivity is based on the probability that a sufficient number of air bubbles will attach to a PVC particle to render it sufficiently buoyant to report to the surface of the slurry from which it is removed by skimmers or the like. [0030] It has been surprisingly discovered that by increasing the temperature of the froth flotation medium, it is possible to dramatically improve both the yield and the purity of the hydrophobic stream in a froth flotation system. This effect is previously unreported in the literature. Accordingly, the present invention is based upon the unexpected discovery that the froth flotation temperature plays a key role in the yield and purity of the product streams from a froth flotation process. THE PROCESS FEED

[0031] The process of the present invention is particularly directed to separating or recovering one or more materials from a mixture of materials, in which the mixture contains one or more materials having the same or similar density as the material(s) of interest. Typically, the mixture or feed is in ground or comminuted form. The feed may include numerous classes of components.

[0032] One large class of components includes plastic-rich mixtures of particles comprising thermoplastic and thermoset polymers, rubber, filled polymers, and other organic and inorganic contaminants.

[0033] Examples of streams utilized as feedstocks in various embodiments of the invention include mixtures of particles generated in the recycling of wire and cable, automotive shredding (i.e. automotive shredder residue , ASR), electronic scrap shredding (electronic scrap residue, ESR), mixed residue from injection molding or extruding operations (i.e. mixed "bleeders"), mixtures of post industrial particles, and mixtures of post consumer particles.

[0034] Depending upon the particular feed, the feed may comprise relatively high proportions of inorganic materials. Examples of such relatively high proportions include at least 50%, i.e. a majority proportion, and even higher proportions such as at least 60% or more.

[0035] Suitable feedstock streams for the preferred embodiment processes typically contain less than 5% of particles with a specific gravity less than 1.0. Such low specific gravity particles can be easily separated by a traditional float-sink operation, rendering the non-floating residue suitable for the techniques of the present invention. FROTH FLOTATION

[0036] In accordance with a preferred aspect of the present invention, suitable feedstock particles are subjected to froth flotation. Froth flotation involves the admixing of feedstock particles with water and air.

[0037] Generally, in accordance with the preferred embodiment processes, a particulate feedstock or feedstock stream is introduced into a froth flotation unit or system. As noted, froth flotation involves the admixing of feedstock particles with water and air. A number of fabricators market froth flotation technology, including Wemco of FLSmidth Dorr-Oliver Eimco USA Inc., of Salt Lake City, UT; Denver, which is available through Metso Minerals of Helsinki, Finland; and Outokumpu Mintek of Helsinki, Finland. Since the air in these units is introduced below the surface of the water, they are referred to as "sub aeration" devices. It is also possible to spray a fluid or a slurry onto the surface of a liquid, generating bubbles. These type of operations are referred to as "spray float". In either case, a stream rich in hydrophobic particles is removed from the surface of the tank, and a stream rich in hydrophilic particles is removed from the bottom of the tank. The removal of particles maybe continuous or dis-continuous.

[0038] The units can be operated as batch, semi-continuous or continuous. They can be operated as single stage or multi-stage. They can be operated at different air flow rates, pressures, etc. They can be arranged into various classes of separation commonly referred to as "roughers", "cleaners" and "scavengers". [0039] The yield and quality of the floating product stream is generally a function of the chemical composition of the particles in the feed mixture, the operating conditions of the froth flotation cell, and the type and quantity of chemicals added to the process to improve yield and selectivity. [0040] In accordance with the present invention, it has unexpectedly been discovered that temperature is an important variable that has a dramatic impact on the yield and selectivity of a froth flotation process.

PREFERRED EMBODIMENT PROCESSES

[0041] The present invention will now be described with respect to reclaiming one or more solid components from a mixture of particles obtained from the recycling of wire and cable insulation. It will be understood that, as noted above, generally any mixture of particles with varying degrees of hydrophobicity can serve as a feedstock for this process.

[0042] A suitable feedstock for the preferred embodiment process comprises untreated wire and cable insulation. Such a material mixture can be obtained by applying various cleaning and float-sink operations such as those described in Patent Publication 2006/0118469 to Bork et al.

[0043] A typical density range for a feedstock mixture suitable for this preferred embodiment process is from about 1.20 to about 1.50 g/cm³. [0044] Such a mixture comprises flexible polyvinyl chloride (PVC), rubber, silicone, and crossed-linked and filled polyethylene. This mixture cannot be further separated by density or specific gravity because the density ranges of each of the types of particles overlaps.

[0045] The mixture of solid particles is admixed with sufficient water to create a slurry of from about 0.1 to about 30 percent by weight solids, and subjected to froth flotation No conditioning step is required. No reaction of the plastic particles with conditioning chemicals to alter the surface state is required. [0046] One or more flotation aids, and specifically hydrophobic organics can be added to the froth flotation system to enhance the flotation of the hydrophobic particles. Suitable organics include various light mineral and vegetable oils. Soy bean oil, linseed oil, and other polyunsaturated oils have been found to be especially effective in this application. Other flotation aids may include one or more salts, that dissolve in the aqueous medium and which serve to alter surface tension of the resulting liquid medium. For other types of feedstocks, other flotation aid chemistries may be more suitable.

[0047] The more hydrophobic particles are removed from the top of the froth flotation tank by skimming or other means, while the less hydrophobic particles are removed from the bottom of the froth flotation tank. Particle removal can be continuous or intermittent.

[0048] In accordance with the present invention, the yield and purity of the floating stream can be manipulated by adjusting the temperature in the froth flotation system. This can be accomplished by using various commercial hot water heaters, heat exchangers, live steam injection, hot or cold water injection, or other means known in the art. Temperatures from about 35°F to about 210⁰F have been found to be useful.

[0049] In general, it has been discovered that increasing the temperature in the froth flotation system tends to increase both the yield and the purity of the most hydrophobic component in the feedstock mixture. However, in some cases, excessive temperatures can result in the floating of some undesirable less hydrophobic components.

[0050] The floating stream from a first froth flotation cell can be deemed final product, or can be subjected to additional froth flotation steps to further improve quality. These additional froth flotation steps can be at the same or a different temperature from the first step.

[0051] In a like manner, the sinking stream from the first froth flotation cell can be deemed final product, or can be subjected to additional froth flotation steps to further improve quality or to recover additional hydrophobic materials. These additional froth flotation steps can be at the same or a different temperature from the first step. [0052] The terms "float product" or "float output" are periodically used herein to refer to one or more outputs of a froth flotation operation which are generally obtained from an upper region and typically from the surface of the liquid medium contained in the vessel. As noted herein, these output(s) typically include higher proportions of the hydrophobic components. Conversely, the terms "sink product" or "sink output" are used to refer to one or more outputs of a froth flotation operation which are generally obtained from a lower region and typically from the bottom of the liquid medium contained in the vessel. These output(s) typically include higher proportions of the hydrophilic components.

[0053] Figure 1 is a schematic illustration of a single froth flotation unit operation or cell 10. The froth flotation unit 10 comprises a vessel 100 adapted to receive at least one feed such as feed 102 and provide outputs, such as first and second outputs 110 and 120. The vessel 100 is adapted to receive at least one feed and provide the noted outputs, and so includes provisions such as inlets, outlets, and connection components. The vessel 100 also is adapted to retain a liquid medium, which is preferably an aqueous liquid. It is also preferred that the vessel include provisions for introducing air into the liquid medium, preferably at one or more lower regions of the vessel so that the air is dispersed relatively uniformly throughout the tank and rises upward from the lower region(s) of the vessel. It is also contemplated to provide provisions for agitating or stirring the aerated liquid medium in the vessel. The vessel 100 may further include one or more screens or filters at the outputs to prevent excessively sized particles or objects from exiting the vessel. As previously noted, the froth flotation unit typically utilizes one or more skimmers or other like assemblies to selectively remove or withdraw particulate material residing in an upper region of the vessel, typically as a result of the froth flotation operation. [0054] The term "aerated" is used herein to refer to the liquid medium of a froth flotation vessel or system receiving air or having previously received air. Typically, such air is administered below the surface of the liquid medium and upon entering the liquid, tends to rise upward in the form of bubbles. The present invention includes other strategies for forming bubbles or otherwise introducing air in a liquid medium of a froth flotation vessel or system. Furthermore, it is contemplated that other gases or vapors may be used instead of air. However, air is preferred in view of its abundancy and essentially free cost.

[0055] A typical operation of the froth flotation cell 10 is as follows. Feed 102 is introduced into the vessel 100. Feed 102 can be in any of the previously described forms, however typically is in the form of a ground or comminuted particulate mixture including at least two types of plastics having the same or similar density, and which are to be separated. The vessel 100 contains an aqueous medium through which air 104 is administered, to form an aqueous aerated medium. [0056] As a result of differences in the hydrophobicity or hydrophilicity characteristics of the various particulates, the particles exhibiting a greater degree of hydrophobicity than other particulates tend to rise in the vessel and collect along or proximate the top surface of the medium. These particulates can be withdrawn or discharged from the vessel 100 as an output 110, i.e. the more hydrophobic product. The particulate exhibiting a greater degree of hydrophilicity than other particulates tend to collect in the lower regions of the vessel, and can be withdrawn or discharged from the vessel 100 as an output 120, i.e. the more hydrophilic product. [0057] Figure 1 also reveals a heater 130 or other thermal input provision. The heater 130 can be incorporated or otherwise mounted within the vessel 100 so as to heat the liquid medium therein, or the heater may be located elsewhere such as along the line providing feed 102. As previously noted, the heater 130 may be in a variety of different forms such as for example, an electrical heater with resistive elements, a steam heater, and/or a heating jacket that provides heat from a heated jacket that circulates a heating fluid in thermal communication with the liquid medium in the froth flotation vessel. Moreover, it will be appreciated that the heater 130 is preferably controlled by one or more temperature controllers as known in the art. [0058] Generally, the liquid medium is heated from an initial temperature within the range of from about 35⁰F to about 100⁰F, and typically, about 45°F, about 5O⁰F, about 55°F, about 60°F, about 65°F, about 70⁰F, about 75°F, or about 80°F; and heated to a temperature within the range of from about 55°F to 180°F, and typically, about 80⁰F, about 90°F, about 100⁰F, about 110°F, about 120°F, about 130°F, about 140 F or about 150°F.

[0059] Figure 2 is a process flow schematic illustrating a froth flotation system 50 comprising a plurality of froth flotation cells. Each cell includes a vessel such as vessels 200, 300, 400, 500, 600, and 700, each of which is a previously described vessel 100. Preferably, each of the vessels 200, 300, 400, 500, 600, and 700 includes one or more heaters for selectively heating the liquid mediums therein. The present invention includes the various vessels being in communication with one or more other vessels in nearly any configuration. It will be appreciated that the configuration depicted in Figure 2 is merely one of potentially many different configurations encompassed by the present invention. With continued reference to Figure 2, the preferred embodiment system 50 will now be described. Feed 202 is introduced to vessel 200, and specifically, to an aqueous aerated medium retained therein. A first output 210 generally containing hydrophobic components, and a second output 220 generally containing hydrophilic components are produced. The second output 220 is fed to the vessel 300 which produces a first output 310 generally containing hydrophobic components, and a second output 320 generally containing hydrophilic components. The second output 320 is fed to the vessel 400 which produces a first output 410 generally containing hydrophobic components, and a second output 420 generally containing hydrophilic components. The first outputs of vessels 200, 300, and 400, i.e. the outputs 210, 310, and 410 generally containing hydrophobic components, are directed as feed to the vessel 500. Introduction of that feed to vessel 500 produces a first output 510 that generally contains hydrophobic components, and a second output 520 that generally contains hydrophilic components. The first output 510 is directed to vessel 600 which produces a first output 610 which generally contains hydrophobic components, and a second output 620 that generally contains hydrophilic components. The first output 610 is directed to vessel 700 which produces a first output 710 which generally contains hydrophobic components, and a second output 720 that generally contains hydrophilic components. The second outputs of vessels 500, 600, and 700, i.e. the outputs 520, 620 and 720 generally containing hydrophilic components, are directed to the vessel 200 and preferably mixed or otherwise combined with the feed 202. Each of the vessels 200-700 preferably receives a supply of air, depicted in Figure 2 as air flows 204, 304, 404, 504, 604, and 704. [0060] Generally, by increasing the temperature of the froth flotation medium, significant increases in the recovery of desired hydrophobic components can be achieved in the floating output product stream(s) of a froth flotation system. For example, increases of about 5% or more in the concentrations of desired hydrophobic components in product yields, can be achieved by increasing the temperature of a froth flotation medium by 20⁰F or more, preferably by heating an additional 1O⁰F to about 20⁰F, and more preferably, by only heating 5°F to about 10°F from the medium's previous temperature. These estimated improvements in yield are with regard to the froth flotation medium being at a temperature in the range from about 55⁰F to about 160⁰F. Increases of about 10% or more in the concentrations of desired hydrophobic components in product yields, can be achieved by increasing the temperature of a froth flotation medium by about 45°F or more, and preferably by heating an additional 25⁰F to about 45⁰F, more preferably 20⁰F to about 25°F, and most preferably by heating only an additional 10°F to 20°F. It will be understood that the correlation between temperature increase and resulting increases in concentration of desired hydrophobic particulates depends upon a host of factors, such as for example, the composition and characteristics of the feed, the flotation medium and whether it includes any additives, and the time periods during which the flotation process is undertaken.

[0061] Thus, generally for many preferred embodiment processes, increases of at least 5% in the concentration of desired hydrophobic materials in a float product stream can be achieved by heating the froth flotation medium at least 20⁰F, preferably at least 10⁰F, and most preferably at least only 5°F. Similarly, increases of at least 10% in the concentration of desired hydrophobic materials in a float product stream can be achieved by heating the froth flotation medium at least 45°F, preferably at least 25°F, more preferably at least 20°F, and most preferably at least only 10⁰F.

[0062] In addition to the various flotation aids noted herein, one or more of the following agents may be used in the froth flotation system to promote separation of the materials. Organic colloids can be used which alter the hydrophilic/hydrophobic surface characteristics of the materials. Suitable examples of organic colloids which can be used in the present invention include tannic acid, a quebracho extract, gelatin, glue, saponin and the like. Other examples of flotation agents include sodium lignin sulfonate and calcium lignin sulfonate. Further examples include pine oil, cresylic acid (also known as xylenol), eucalyptus oil, camphor oil, a derivative of a higher alcohol, methylisobutyl carbinol, pyridine, o-toluidine and the like. Yet another example of a suitable agent is sodium silicate. It is also contemplated that one or more surfactants such as those described in US Patent 5,377,844 could be utilized. Furthermore, depending upon the liquid medium used and the composition of the feed, it may also be possible to utilize one or more of the following agents: polyoxyparafins, alcohols such as methyl isobutyl carbinol (MIBC), and various polyglycols.

[0063] In addition to increasing the yield of desired hydrophobic particulates in a float product stream in a froth flotation operation, the present invention also provides techniques for increasing the yield of desired hydrophilic particulates in a sink product stream in a froth flotation operation. That is, it has been surprisingly discovered that by heating a liquid medium of a froth flotation vessel or system improved recovery of hydrophilic materials can also be achieved. As will be appreciated, hydrophilic materials can be recovered in one or more sink product or outputs of a froth flotation system. Moreover, it has also been surprisingly discovered that heating the liquid medium can also result in reducing the concentration of contaminants in a float output or product stream in a froth flotation operation.

EXAMPLES

[0064] The various preferred embodiment aspects will be better understood by reference to the following examples which serve to illustrate but not to limit the present invention.

[0065] A feedstock was derived from the reclamation of insulation from recycled wire and cable, previously separated, to create a mixed stream of particles in the density range of 1.2 to 1.50 g/cm³. The particles included PVC, rubber, silicone, and filled polyethylene.

[0066] Feedstocks derived from various suppliers were subjected to three froth flotation cells using a spray float type apparatus. Each froth flotation operation utilized 100 grams of feedstock and 0.1 grams of emulsified soy bean oil as a flotation aid. Each operation was conducted at a different range of temperatures to demonstrate the impact of froth flotation temperature on hydrophobic product yield and quality.

[0067] The floating and sinking products were all dried and weighed to determine yield.

[0068] The floating products were then subjected to analytical testing to determine the percentage of contaminants (i.e. rubber, silicone, and filled PE) that were present in that product. Results are presented in Table 1 , below. Table 1

[0069] Figures 3-8 are graphical illustrations of the data presented in Table 1. [0070] Figure 3 is a graph of data presented in Table 1 for feedstock No. 1 illustrating the relationship between increasing concentration of a desired component in a float product as temperature of a liquid medium increases. Figure 3 illustrates that for the particular mixture of materials in feedstock No. 1 , yields of PVC in the hydrophobic or float stream, tend to increase with higher froth flotation temperatures. Greater incremental yield increases were observed at higher temperatures. [0071] Figure 4 is a graph of data presented in Table 1 for feedstock No. 1 illustrating the relationship between decreasing concentration of a contaminant component in the float product as the froth flotation temperature of the liquid medium increases. Figure 4 reveals that higher froth flotation temperatures for the feedstock No. 1 led to improved reductions in contaminant concentration levels in the float product.

[0072] Figure 5 is a graph of data presented in Table 1 for feedstock No. 2 illustrating the relationship between increasing concentration of a desired component in a float product as the froth flotation temperature of a liquid medium increases. As with previously described Figure 3, here it can be seen that greater yields in the float stream can be obtained by using higher froth flotation temperatures. [0073] Figure 6 is a graph of data presented in Table 1 for feedstock No. 2 illustrating the relationship between decreasing concentration of a contaminant component in a float product as the froth flotation temperature of a liquid medium increases. As in previously described Figure 4, higher froth flotation temperatures for feedstock No. 2 led to improved reductions in contaminant concentration in the float product.

[0074] Figure 7 is a graph of data presented in Table 1 for feedstock No. 3 illustrating the relationship between increasing concentration of a desired component in a float product as temperature of a liquid medium increases. Figure 7 illustrates that in feedstock No. 3, greater yields in the float stream generally increased by use of higher froth flotation temperatures. However, the plot of Figure 7 suggests that for this particular system, an optimal temperature for the froth flotation medium is likely in the range of from about 100⁰F to about 140⁰F.

[0075] Figure 8 is a graph of data presented in Table 1 for feedstock No. 3 illustrating the relationship between decreasing concentration of a contaminant component in a float product as temperature of a liquid medium increases.

[0076] Many other benefits will no doubt become apparent from future application and development of this technology.

[0077] All patents, published applications, and articles noted herein are hereby incorporated by reference in their entirety.

[0078] As described hereinabove, the present invention solves many problems associated with previous processes and separation techniques. However, it will be appreciated that various changes in the details, materials and operations or steps, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the principle and scope of the invention, as expressed in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A froth flotation process for forming from a particulate feed, a first output including hydrophobic particulates of a first material and a second output including less hydrophobic particles of a second material, the first material and the second material having the same or similar densities, the process comprising: adding the particulate feed to an aqueous aerated medium; heating the aqueous medium whereby the yield of the hydrophobic particles of the first material in the first output is increased.

2. The froth flotation process of claim 1 wherein the first material is polyvinyl chloride.

3. The froth flotation process of claim 1 further comprising: adding a froth flotation additive to the aqueous medium to promote the yield of the hydrophobic particles of the first material in the first output.

4. The froth flotation process of claim 3 wherein the flotation additive includes an agent selected from the group consisting of mineral oil, vegetable oil, and combinations thereof.

5. The froth flotation process of claim 1 wherein heating is performed so that the aqueous medium is at a temperature of from about 35°F to about 210⁰F.

6. The froth flotation process of claim 1 wherein the adding and heating operations are performed in a first froth flotation stage, the process further comprising; directing the first output to a second froth flotation stage in which the first output is added to a second aqueous medium of the second stage to form a third output including hydrophobic particles of the first material.

7. The froth flotation process of claim 6 wherein the temperature of the aqueous medium of the first froth flotation stage is different than the temperature of the second aqueous medium.

8. The froth flotation process of claim 1 further comprising: adding one or more salts to the aqueous medium to change the surface tension of the aqueous medium.

9. The froth flotation process of claim 1 wherein the particulate feed comprises a majority of inorganic materials.

10. The process of claim 1 wherein heating is performed to raise the temperature of the aqueous medium by at least 5°F whereby the concentration of the first material in the first output is increased by at least 5%.

11. The process of claim 10 wherein the temperature of the aqueous medium is raised at least 10⁰F.

12. The process of claim 11 wherein the temperature of the aqueous medium is raised at least 20⁰F.

13. The process of claim 1 wherein heating is performed to raise the temperature of the aqueous medium by at least 10⁰F whereby the concentration of the first material in the first output is increased by at least 10%.

14. The process of claim 13 wherein the temperature of the aqueous medium is raised at least 20⁰F.

15. The process of claim 14 wherein the temperature of the aqueous medium is raised at least 25°F.

16. The process of claim 15 wherein the temperature of the aqueous medium is raised at least 45°F.

17. A method for increasing recovery of hydrophobic materials in a first output of a froth flotation system, the froth flotation system comprising a vessel adapted to retain an aqueous aerated medium and produce the first output and a second output, the first output including a greater proportion of hydrophobic materials than the second output, the method comprising: introducing a particulate feed to an aqueous medium in a froth flotation system, the particulate feed including at least two materials differing in hydrophobicity; heating the aqueous medium whereby the proportion of hydrophobic materials in the first output is increased.

18. The method of claim 17 wherein the at least two materials include a first plastic material and a second plastic material.

19. The method of claim 18 wherein the first and the second plastic materials have a density within the range of from about 1.2 to about 1.5 g/cm³.

20. The method of claim 17 wherein upon introducing the particulate feed to the aqueous medium, the solids content of the medium is within the range of from about 0.1 % to about 30% by weight.

21. The process of claim 17 wherein heating is performed to raise the temperature of the aqueous medium by at least 5°F whereby the concentration of the first material in the first output is increased by at least 5%.

22. The process of claim 21 wherein the temperature of the aqueous medium is raised at least 10⁰F.

23. The process of claim 17 wherein heating is performed to raise the temperature of the aqueous medium by at least 10⁰F whereby the concentration of the first material in the first output is increased by at least 10%.

24. The process of claim 23 wherein the temperature of the aqueous medium is raised at least 20⁰F.

25. A method for increasing recovery of hydrophilic materials in a second output of a froth flotation system, the froth flotation system comprising a vessel adapted to retain an aqueous aerated medium and produce a first output and the second output, the second output including a greater proportion of hydrophilic materials than the first output, the method comprising: introducing a particulate feed to an aqueous medium in a froth flotation system, the particulate feed including at least two materials differing in hydrophilicity; heating the aqueous medium whereby the proportion of hydrophilic materials in the second output is increased.

26. The method of claim 25 wherein the at least two materials include a first plastic material and a second plastic material.

27. The method of claim 26 wherein the first and the second plastic materials have a density within the range of from about 1.2 to about 1.5 g/cm³.

28. The method of claim 25 wherein upon introducing the particulate feed to the aqueous medium, the solids content of the medium is within the range of from about 0.1 % to about 30% by weight.

29. The process of claim 25 wherein heating is performed to raise the temperature of the aqueous medium by at least 5°F whereby the concentration of the first material in the first output is increased by at least 5%.

30. The process of claim 29 wherein the temperature of the aqueous medium is raised at least 1O⁰F.

31. The process of claim 25 wherein heating is performed to raise the temperature of the aqueous medium by at least 10⁰F whereby the concentration of the first material in the first output is increased by at least 10%.

32. The process of claim 31 wherein the temperature of the aqueous medium is raised at least 20⁰F.

33. A method for reducing the concentration of contaminants in a first output of a froth flotation system, the froth flotation system comprising a vessel adapted to retain an aqueous aerated medium and produce the first output and a second output, the first output including a greater proportion of hydrophobic materials than the second output, the method comprising: introducing a comminuted feed to an aqueous medium in a froth flotation system, the feed including at least two materials differing in hydrophobicity; heating the aqueous medium whereby the concentration of contaminants in the first output is decreased.

34. The method of claim 33 wherein the at least two materials include a first plastic material and a second plastic material.

35. The method of claim 34 wherein the first and the second plastic materials have a density within the range of from about 1.2 to about 1.5 g/cm³.

36. The method of claim 34 wherein upon introducing the particulate feed to the aqueous medium, the solids content of the medium is within the range of from about 0.1 % to about 30% by weight.

37. The process of claim 33 wherein heating is performed to raise the temperature of the aqueous medium by at least 5°F whereby the concentration of the first material in the first output is increased by at least 5%.

38. The process of claim 37 wherein the temperature of the aqueous medium is raised at least 10⁰F.

39. The process of claim 33 wherein heating is performed to raise the temperature of the aqueous medium by at least 10⁰F whereby the concentration of the first material in the first output is increased by at least 10%.

40. The process of claim 39 wherein the temperature of the aqueous medium is raised at least 20⁰F.

41. A method for separating a first plastic from a particulate mixture including the first plastic and at least another plastic having the same or similar density, the method free of any preconditioning or pretreatment operation in which the first plastic is exposed to a conditioning agent, the method comprising: providing a froth flotation system comprising a vessel and an aqueous aerated medium disposed in the vessel; adding the particulate mixture to the aqueous aerated medium whereby a first output including a majority of the first plastic is produced; wherein the temperature of the medium is at least 90⁰F.

42. The method of claim 41 wherein the temperature of the medium is at least 100⁰F.

43. The method of claim 42 wherein the temperature of the medium is at least 110⁰F.

44. The method of claim 43 wherein the temperature of the medium is at least 120⁰F.

45. The method of claim 44 wherein the temperature of the medium is at least 130⁰F.

46. The method of claim 45 wherein the temperature of the medium is at least 140°F.