RU2721731C1 - Method of leaching and extraction of gold and silver from pyrite cinder - Google Patents

Abstract

FIELD: technological processes; mining.SUBSTANCE: group of inventions relates to processing of gold-bearing and silver-bearing wastes of ore-dressing plants. Pyrite refuses are processed by agitation leaching of pyrite cinder with extraction of gold and silver. At cascade of wet grinding mills super-fine grinding of pyrite cinder to fraction of 5–8 mcm is carried out, then in form of water-containing pulp they are supplied to reactors for agitation leaching with mixing by means of double hydrodynamic impellers. Leaching of pulp is carried out at supersonic speed with solution of thiourea with concentration of 0.1 % with sulfuric acid with concentration of 0.5 %. Sludge formed after leaching is washed from productive solution and in form of wet cake is supplied to vacuum ceramic filter for dehydration. Dehydrated cake is used for cement production. Productive solution containing gold and silver is subjected to electrolysis for extraction of gold and silver, after which the productive solution is returned into the production cycle into the water-containing pulp.EFFECT: inventions enable to carry out environmentally safe fast efficient leaching and extraction of gold and silver from pyrite cinder.6 cl, 8 dwg, 3 tbl

Description

The group of inventions relates to the metallurgy of non-ferrous, noble metals, in particular to methods for processing gold-containing and silver-containing waste from mining and processing enterprises, as well as non-waste manifestations of this method.

Three types of pyrite cinders are distinguished (pyrite cinders, cinders from flotation tailings of sulfide ore dressing, carbon cinders), which differ significantly from each other both in chemical composition and physical characteristics.

Pyrite concentrates (from sulphide ore tailings) and pyrite cinders (from pyrites) are valuable types of technogenic mineral and chemical resources stored by mining and processing plants (GOK) in the enrichment of sulfide copper and lead-zinc raw materials and, accordingly, accumulated chemical metallurgical enterprises during the period of production of sulfuric acid from the initial pyrite raw material - sulfur pyrite (FeS2). Pyrite cinder (from pyrites) is a fine crumbly powder of dark brown color. Hazard Class - IV. Pyrite cinders contain gold, silver and a number of other elements.

Today, a rational technology for the use of these wastes, which provides the integrated extraction of iron, non-ferrous and precious metals, is unknown. To date, more than 250 million tons of pyrite concentrates (from tailings) and 30 million tons of pyrite cinders (from pyrites) have been accumulated in Russia. Under the influence of precipitation, many highly toxic compounds are washed out of pyrite concentrates and pyrite cinders, which have a detrimental effect on the environment.

There are scientific developments and registered patents for the processing of pyrite cinders, but are not used in production due to the toxicity and complexity of the technology.

          According to the patent RU 2659505 (application 2017131341, September 6, 2017), a method for processing pyrite cinders is known, in which the pelletizing operation is carried out sequentially using 95.998% sulfuric acid as a binder, subsequent firing of the pellets at a temperature of 250-300 ° C for 20 minutes, leaching fired pellets in an ultrasonic field with a wide spectrum of frequencies and a power density of 0.5h1.0 W 3cm-3 for 15h30 min at (50h55) ° C, filtering the solution, directing the formed cakes to extract precious metals, isolating copper from the liquid phase by carburizing on iron, fractional precipitation of non-ferrous and rare metal hydroxides from it, salting out of ethanol from a solution in a ultrasonic field of chemically pure hydrogen sulfate, its subsequent dissolution in water and precipitation from a solution of iron (II) hydroxide by alkalization with ammonia to pH (9h9.5) .

This method is rather complicated and is aimed primarily at the allocation of iron, and not non-ferrous and precious metals.

According to patent RU 2397260 (application 2009108888/02, 03/10/2009), there is a method for processing pyrite cinders containing non-ferrous, noble and ferrous metals, with their extraction, including leaching of non-ferrous metals from the cinder and subsequent extraction from the leach cake of noble metals, characterized in that leaching is carried out by a bacterial complex consisting of four types of acidophilic thionic bacteria in the active phase of growth with the cultivation of microorganisms in solution and their accumulation during the creation of a weakly acidic environment and the active oxidation of pyrite with the conversion of iron, copper, zinc, arsenic, lead and antimony into the liquid phase at a rate of iron oxidation of 24-26 g / l per day.

 The disadvantage of this method is its complexity associated with high environmental friendliness: the use of acidophilic thionic bacteria in industrial rather than laboratory conditions, significantly complicates

production processes entails their unpredictability and instability.

According to patent RU 2398034 (application 2009111738/02, March 30, 2009), a method for processing sulfide gold-containing arsenic-antimony concentrates or ores is proposed, which includes preparing a mixture from arsenic-antimony concentrates or ores with a halide, calcining the charge with the release of gaseous compounds and their condensation and obtaining a gold-containing cinder and leaching gold from it, characterized in that the mixture is prepared from concentrate or ore and ammonium chloride and / or fluoride in a mass ratio of 10: 0.3-3.0, firing is carried out in a constant stream of non-oxidizing gas to obtain a gold-containing pyrrhotite cinder, gold leaching is carried out by sorption cyanidation of a gold-containing pyrrhotite cinder, and gaseous compounds in the form of gaseous antimony sulfide and arsenic polysulfides, isolated during firing, are subjected to fractional condensation.

The disadvantage of this patent is the need to use cyanides, which cause significant harm to the environment, have special conditions of storage and use.

The technical result of the proposed solution is environmentally friendly, fast, efficient leaching and extraction of gold and silver from pyrite cinders (from pyrites):

                                                      Thiourea (thiocarbonate diamide) has the following properties:

- Molecular formula of thiourea CH4N2S

- The molecular weight of thiourea is: 76.12

          - The density of the crystals is extremely low: 1.405 g / cm3

- Thiourea hazard class: VI

       - The quality of thiourea is regulated by state document GOST 6344 73 "Reagents. Thiourea. Technical conditions."

Transporting thiourea, according to GOST 6344 73, is allowed by all means of transport. Shelf life is 12 months from the date of production.

The chemical properties of thiourea are valued at mining plants, in agriculture, in the textile industry, metallurgy, and pharmaceuticals. 10-15 years ago, thiourea was used as a preservative for fresh citrus fruits.

The proposed method of this technology is that the leaching and extraction of gold and silver from pyrite cinder is carried out using thiourea (formula CH4N2S), while thiourea is used in aqueous pulp mixed with other reagents. With this method, thiourea is used instead of cyanides. This technology has not yet been used in production so far in Russia and abroad.

   Of all the methods known to the applicant (gravity concentration, cyanidation, bio-opening), the use of thiourea for leaching precious metals from pyrite cinders gives the highest rates, where the extraction of precious metals has increased and is from 70% or more.

The implementation of the invention is illustrated by the following examples,

not wearing, however, restrictive. The purpose of the mineralogical and technological study of pyrite cinder (from pyrites) with the rationale for a rational processing technology: leaching and extraction of precious metals using thiourea.

Chemical analysis of the initial sample was carried out at the Analytical Center of Gipronickel Institute LLC (accreditation certificate No. POCC RU. 0001.510042).

The content of gold and silver was monitored by assay method in the laboratory of the Scientific Research Center "Hydrometallurgy" LLC (accreditation certificate No. AAC.A.00254).

 The content of precious metals was determined by inductively coupled plasma spark mass spectrometry (JMS-BM2 dual-focus mass spectrometer manufactured by JEOL, Japan) in the laboratory of nuclear-physical and mass-spectral analysis methods of the Institute of Problems of Microelectronics Technology and High-Purity Materials (accreditation certificate No. ROSS RU. 0001.513800).

The yield of material fractionated by size was determined after drying using laboratory electronic scales of the MW-T 150x0.001g and CASBEE 1200x 0.1g brands (certified by the State Standard of the Russian Federation).

For optical research methods the following were used: ECLIPSE-POL polarizing microscope, SMZ-1500 optical stereo microscope, equipped with the DS-5M-LI digital microphotographic system. Quanta 650 SEM scanning electron microscope equipped with the Genesis energy dispersive microanalysis (EDAX) system.

 Native gold was visualized mainly in the superheavy non-magnetic fraction of the concentrate (Fig. 18) and in isolated cases in the superheavy non-magnetic fraction of the intermediate 1. Some parts were examined under an electron microscope (see Fig. 18 c-h).

 Native gold has a bright yellow, sometimes brownish-yellow color due to the development of iron hydroxide films on the surface of particles. The shape of the grains is predominantly interstitial with imprints of other minerals, less often isometric; the surface of interstitial particles is embossed, the isometric ones have a smooth, weakly manifest embossed surface. The size of the visualized particles is 10-100 microns, 20-50 microns prevail.

The shape of the particles indicates that native gold is an independent mineral phase that crystallized along with primary sulfide minerals; it is not a part of pyrite and other sulfides in the form of an isomorphic impurity, and, most likely, is associated with them in the form of submicroscopic and microscopic inclusions.

The chemical composition of native gold determined by microprobe analysis is given in Table 1. According to the classification of Petrovskaya N.V. native gold belongs to high-grade and partially high-grade.

The impurity element in the composition of the mineral is silver, the content of which is 2.55–9.56%.

                                            Table 1

              The chemical composition of native gold particles

No. p / p % Content Amount% Note  Au  Ag  1 97.45 2,55 100.00 FIG. 3,1  2 92.86 7.14 100.00 FIG. 3.2  3 93.32 6.68 100.00 FIG. 3.3  4 90.44 9.56 100.00 FIG. 3.4  5 95.29 4.71 100.00 FIG. 3,5  6 94.12 5.88 100.00 FIG. 3.6

   The chemical composition of the pyrite cinder sample (Table 2) was determined by traditional chemical analysis, and the gold and silver contents by the assay method.

                                             table 2

The chemical composition of the initial pyrite cinder (from pyrites)

Component Original sample Content% SiO2 19.19 TiO2 0.10 Al2O3 2.47 Fe total. / Fe204 total., Including: 48.08 / 68.78 CaO 0.46 MgO 0.73 MnO 0.05 K2O 0.16 Na2O 0.14 P2O5 0.01 S total 1,11 Ba 2.20 Cu ** 0.31 / 0.30 Zn ** 0.61 / 0.55 As ** 0.20 / 0.15 Pb ** 0,14 / 0,11 Au *, g / t 2.00 Ag *, g / t 28.80 Amount 98.56

   Leaching of precious metals from pyrite cinders was carried out using two different reagents (in comparison) - a) traditional potassium cyanide and b) thiourea.

      A) Parameters of the process of leaching of precious metals from the initial pyrite cinder using potassium cyanide: ratio T: W = 1: 4, the fineness of the material is 0.1 mm; duration is 24 hours; coal loading - 5% of the volume of the liquid phase of the pulp; the concentration of calcium cyanide is 2.0 g / l; the pH is 10.5. The consumption of cyanide during the leaching of precious metals from the initial pyrite cinder was 14.2 kg / t.

B) Parameters of the process of leaching of precious metals from the initial pyrite cinder using thiourea: the fineness of the material is 0.1 mm; duration is 24 hours; coal loading - 3% of the volume of the liquid phase of the pulp; thiourea concentration -0.1%; concentration of H2SO4 –0.5%; the concentration of ferric sulfate is 0.07%. The consumption of thiourea for leaching of precious metals from the initial pyrite cinder was 5.55 kg / t.

  Table 3

The results of the leaching of precious metals from the initial pyrite cinder using potassium cyanide and thiourea.

  1) Leaching using potassium cyanide

Name
product   Cake yield,% Content, g / t
Au ag Recovery%
Au ag Resin 96.80 1.00 12.50 51.60 45.12 Leaching cake 96.80 1.00 16.30 48.40 54.79 Original sample 96.80 2.00 28.80 100.00 100.00

 2) Leaching using thiourea

Name
product Output
cake,% Content, g / t
Au ag Recovery%
Au ag Coal 95.92 1.38 70.93 Kek
leaching 95.92 0.60 29.07 Original sample 95.92 1.98 100.00

      An analysis of the data showed that the proportion of cyanated gold and silver in the initial pyrite cinders is 51.60% and 45.21%, respectively. When processing initial pyrite cinders and leach cake with thiourea, the fraction of recoverable gold is 70.93%, which is significantly higher than when using cyanide.

Significantly higher rates of gold recovery using thiourea (from the initial pyrite cinder - 70.93%) compared with cyanidation are due to several reasons: the rate of gold leaching in the presence of thiourea is 10 times higher; thiourea is less susceptible to impurity ions; Gold dissolves more effectively in acidic solutions in the presence of an oxidizing agent. An important role is played by the fact that thiourea is much more environmentally friendly than cyanides. For cyanides, the hazard class is I, and for thiourea, the hazard class is VI.

       Huge amounts of money are spent on the disposal of cyanides and problems may occasionally arise from supervisory structures.

Thiourea is environmentally friendly.

         Pyrite cinders as a raw material for the cement industry (pyrite cinders serve as an additive to the mixture for cement production) after leaching (the main leaching reagent is thiourea) and the extraction of precious metals will be sold to cement plants, which indicates non-waste production.

       Thiourea in the form of pulp again enters the processing process (closed cycle).

The following images (figures) are attached to the application, explaining the results of Table 1:

FIG. 1 - Native gold particles visualized in a Gemeni concentrate, image under a stereo microscope;

     FIG. 2 - Native gold particles isolated from a non-magnetic superheavy fraction of Gemeni concentrate, image under a stereo microscope;

FIG. 3.1-3.6 - Native gold particles isolated from non-magnetic heavy fraction of Gemeni concentrate, image in backscattered electrons.

           The technological scheme for the processing of pyrite cinders can be briefly presented as follows:

1) Pyrite cinders are already crushed and calcined raw materials, well prepared for processing. At the first stage, pyrite cinders are loaded by a loader into a bunker equipped with grate grates to separate large lumps, iron scrap, etc., and garbage brought into storage. Then by transport

the tape goes to the grinding department - a cascade of super-fine grinding wet mills.

2) The cinders passed through the disintegrator enter the cascade of super-fine grinding wet mills, where the raw materials in the aqueous medium are super-fine crushed to a fraction of 5-8 microns.

3) After super-fine grinding, with the help of pumps, the pulp is pumped through the slurry line to the leaching compartment. Where the main reagent for conducting chemical processes is thiourea (CH4N2S). Prepared in special containers (vats), the reagents are fed into the reactors for agitation leaching. Leaching reactors are mixing tanks, which are carried out using dual hydrodynamic impellers located in the center.

Pulp leaching occurs when the main reagent, thiourea and other reagents, is fed at supersonic speed in order to obtain maximum mass transfer efficiency and ensure effective oxidation of pyrite cinders.

Leach reactors are used in conjunction with the modular and easy to install Zipa Tanks. Zipa Tank is a tank for storing reagents, sludge, pulp, concentrates, etc. After the process, the pulp from the reactors enters the thickener.

5) Thickener - apparatus for carrying out the thickening process. Condensation is the process of preparing sludge in order to give them the necessary thickness before further processing (enrichment, dehydration).

6) The thickened sludge is pumped to the filter press to wash off the productive solution, and then the washed wet cake is fed to a vacuum KDF (Vacuum Ceramic Filter) for effective dehydration. Humidity cake after dehydration 7-9%. After dehydration, the cake is stored by a loader in a prepared room and loaded into big bags, after which it is sent to cement plants.

7) After the thickener, filter press and CDF, the productive solution is returned back to the cycle, for additional saturation with precious metals. After several saturation cycles, the solution is pumped to flow electrolysis using a pump to separate gold and silver. After electrolysis, the solution is cleaned of impurities, further strengthened and returned back to the cycle. Gold and silver are smelted, where they make the Dore alloy (a gold-silver alloy), which is supplied to a refinery for the separation and production of pure metal ingots.

Considering that pyrite cinders themselves are considered production waste, and given that the technology involves the reuse of sludge in another industry, it can be argued that the proposed method for this technical field can be considered waste-free production.

Claims (6)

1. A method of processing pyrite cinders, including agitation thiourea leaching of pyrite cinders with the extraction of gold and silver, characterized in that on the cascade of wet mills, super fine grinding of pyrite cinders to a fraction of 5-8 microns is carried out, after which they are fed into the reactors in the form of a water-containing pulp agitation leaching with mixing by means of twin hydrodynamic impellers, while the leaching of pulp is carried out at a supersonic speed with a solution containing 0.1% thiourea CH ₄ N ₂ S and 0.5% sulfuric acid, and the productive solution formed after leaching contains gold and silver , subjected to electrolysis to highlight gold and silver. 2. The method according to p. 1, characterized in that the productive solution enters the electrolysis after several cycles of leaching. 3. The method according to p. 2, characterized in that the electrolysis of the productive solution is carried out in a flowing electrolyzer. 4. A method of processing pyrite cinders, including agitation thiourea leaching of pyrite cinders with the extraction of gold and silver, characterized in that on the cascade of wet mills, super fine grinding of pyrite cinders to a fraction of 5-8 microns is carried out, after which they are fed into the reactors in the form of a water-containing pulp for agitation leaching with mixing by means of twin hydrodynamic impellers, while the leaching of pulp is carried out at a supersonic speed with a 0.1% thiourea solution with a sulfuric acid concentration of 0.5%, the sludge formed after leaching is washed from the productive solution and fed to a vacuum cake a ceramic filter for dehydration, after which the dehydrated cake is used for cement production, and the resulting productive solution containing gold and silver is electrolyzed to separate gold and silver, after which the productive solution is returned to the production cycle in water pulp. 5. The method according to p. 4, characterized in that the productive solution enters the electrolysis after several leaching cycles. 6. The method according to p. 5, characterized in that the electrolysis of the productive solution is carried out in a flowing electrolyzer.

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