RU2353763C1 - Method of underground leaching of precious metals out of ores - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention refers to mining of minerals by means of chemical-technological methods. The method of underground leaching of precious metals from ores of water-permeable gravel deposits and auriferous gravel, and also from residual soils consists in boring a system of injection and evacuation boreholes, in pumping oxidant and leaching solution into an ore bearing bed, in withdrawing production solution, in processing it with known methods of cementing and sorption. Processing of ore is performed in two stages. During the first stage ore bearing bed is oxidised with oxygen by means of watering it with softened circulating solution saturated with oxygen containing gas. The injection solution is preliminary cleared from suspension of salts of hardness and impurities. During the second stage copper ammine and thiosulfate are added to evacuation solution, pH and contents of sulphite is corrected with sulphuric acid and ammonia. Precious metals are oxidised and leached with this mixture.

EFFECT: implementation of ecologically clean thiosulfate leaching of precious metals under bed conditions.

5 cl, 5 ex

Description

The invention relates to the field of mining by chemical-technological methods. It can be used in the extraction of precious metals from buried placers, weathering crusts and complex gold deposits that are in favorable hydrogeological conditions.

The tendency in the mining industry to reduce the content of rare and precious metals in ores, as well as the complex hydrogeological conditions of the deposits, inevitably led to the development of underground leaching (PV) methods. The main criteria for the applicability of these methods in practice are extraction efficiency and environmental safety.

Employees of Irgiredmet in 1977 for the first time tested the PV method of noble metals from placer ore in Yakutia. Despite the encouraging results of the experiment, the method was not developed due to the toxicity of the reagent and the inevitable pollution of groundwater outside the mining allotment.

Known chlorine-chloride method PV noble metals (RF patent 2074998, 1994, prototype). The method is mastered on an industrial scale at two fields. As of 01.01.06, 320 kg were mined at the Tatar deposit, and 89 kg of gold at the Maminskoye deposit (Mineral Resources No. 2, 2007). Environmental safety during mining of the ore zone is ensured by the creation of hydrochemical barrage systems that prevent the spreading of industrial solutions outside the operating area (RF patent 2098619, 1997).

The disadvantages of the method stem from the complexity of handling the reagent and processing of aggressive productive solutions.

Known thiosulfate method of heap leaching of precious metals from oxidized ores (patent R. Kazakhstan 1873, analogue). The method is practiced on an industrial scale at the Zherek deposit (Mining Journal, 2001, No. 11, 90). Of all the methods for extracting precious metals from ores, it is recognized as the most environmentally safe.

Known two-stage method of downhole PV of uranium (US patent 4376098, analogue). The ore-containing formation is first worked out with a solution of hydrochloric or other acids without an oxidizing agent, and then uranium is leached with sulfuric acid with an oxidizing agent. Preliminary hydrochloric acid treatment of the formation is aimed at dissolving some minerals of alkaline earth metals and iron. As a result of this, at the subsequent leaching stage, the filtration permeability increases, the contact of the beneficial component with sulfuric acid improves, which contributes to obtaining a higher uranium recovery coefficient.

The technical task of the proposed method is the use of environmentally friendly thiosulfate leaching of noble metals in reservoir conditions. It is achieved by pre-oxidizing the host rocks and improving the permeability of the formation.

The essence of the method consists in the sequential use of two oxidizing agents: oxygen and copper oxide in the form of a copper-ammonia complex. The whole process of mining the ore-bearing formation is divided into two stages. On the first, the host rocks are oxidized with oxygen by flooding with a softened formation solution having pH = 8-10, saturated with oxygen-containing gas, on the second, the noble metals are actually leached also at pH = 8-10 with a thiosulfate-ammonia solution that contains oxide copper.

The full technological cycle for the extraction of precious metals by the proposed method is divided into 10 main operations:

- softening pumping solutions by adding an alkaline reagent;

- clarification of the injection solution from suspension;

- saturation of the clarified solution with oxygen-containing gas;

- oxidation of ore-bearing rock by flooding with an oxygen-containing solution;

- preparation of a leaching thiosulfate solution;

- preparation of a solution of copper ammonia;

- the introduction of solutions of copper thiosulfate and ammonia in a circulating solution;

- pH adjustment of the leach mixture;

- leaching of precious metals with a thiosulfate-ammonia mixture;

- pumping productive solution and its processing.

Processing the productive solution to obtain the final product involves several more operations, but this part of the technology belongs to another independent field.

The chemical processes accompanying the softening of formation waters are well known from the water treatment technology of boiler water and the carbonate method of PV uranium. They are based on the exchange reactions of dissolved hardness salts with alkaline agents: ammonia, carbonates and alkali metal hydroxides. The resulting crystalline precipitates of carbon dioxide salts of alkaline earth metals and amorphous hydrates of iron and aluminum are separated from the solution by sedimentation and / or filtration.

Another softening option is based on ion-exchange processes using sulfonated coal or cation-exchange resins. This method is also widely practiced in water treatment on an industrial scale and does not require explanation.

The saturation of the clarified solution with an oxygen-containing gas is achieved by the known Froth-flow method (foam stream), first used by Union Carbide at the uranium uranium oxide plant.

There are numerous designs of downhole type gas saturators, including domestic ones (USSR AS 1571828, 1988).

The solubility of an oxygen-containing gas (g, mg / l) at the bottom of the injection well for pressures from 1 to 100 at and temperatures from 0 to 40 ° C is satisfactorily described by the equation

The amount of gas-saturated solution, which is necessary for their oxidation at specific hydrogeological parameters, is calculated by the oxidation value of the rocks of the ore-bearing formation.

For practical purposes, technical oxygen can be used, which is supplied in auto-recipients of TRCs, or oxygen-enriched air obtained in air separation units (ASUs), which, in particular, are produced by Russian companies RANKO, GRASYS and NPF TESORB.

The oxidation of some of the most important minerals of the host rocks - pyrite and chalcopyrite in a slightly alkaline solution at the first stage of mining is described by the following equations:

2FeS ₂ + 15 / 2O ₂ + 8OH ^- → Fe ₂ O ₃ + 4SO ₄ ^2- + H ₂ O;

CuFeS ₂ + 17 / 4O ₂ + 4NH ₃ + 2OH ^- → Cu (NH ₃ ) ₄ ²⁺ + 1 / 2Fe ₂ O ₃ + 2SO ₄ ^2- + H ₂ O

If the formation water contains hydrogen sulfide or sulfide ion as a decomposition product of organic matter, then they also undergo sequential oxidation:

2S ^2- + 2O ₂ + H ₂ O → S ₂ O ₃ ^2- + 2OH ^-

S ₂ O ₃ ^2- + 2OH ^- + 2O ₂ → 2SO ₄ ^2- + H ₂ O

At the stage of dissolution of precious metals from ore, the following reactions proceed:

Au + 5S ₂ O ₃ ^2- + Cu (NH ₃ ) ₄ ²⁺ → Au (S ₂ O ₃ ) ₂ ^3- + Cu (S ₂ O ₃ ) ₃ ^5- + 4NH ₃

The thiosulfate complex of gold is stable in the range of pH = 8.5-10.5 and has an instability constant of 4 · 10 ^-30 . Oxidation proceeds at an oxidizing potential of 0.15-0.2 V.

Silver dissolves in a similar way, but its thiosulfate complex is less stable and has an instability constant of 3.5 · 10 ^-14 .

The formation of the copper-ammonia complex proceeds according to the reaction

Cu ²⁺ + 4NH ₃ → [Cu (NH ₃ ) 4] ²⁺

The instability constant of the complex is 5 · 10 ^-10 .

This complex in the process of reduction in a thiosulfate medium undergoes a change:

The novelty of the proposed method consists in the use of thiosulfate leaching of noble metals in reservoir conditions. This becomes possible due to the preliminary oxidation of the host rocks with oxygen and the extraction of hardness salts from the formation water. These measures, on the one hand, facilitate the oxidation of noble metals in the presence of a complexing agent, and on the other hand, improve the filtration permeability of the rocks with respect to the leaching solution.

The advantages of the method over the existing chloride-chloride are the greater environmental safety of the reagent, the implementation of the process in a slightly alkaline environment, allowing you to have the whole range of equipment in a non-corrosive design, and the use of air oxygen - cheap and affordable in the required amount in any region.

The profitability of the method will be determined by the presence in the ore of sulfides, in particular pyrite, iron oxides and other reducing agents that require oxidation. The presence of chalcopyrite and others and copper minerals in the ore can significantly reduce the consumption of copper sulfate and simplify the technology.

The main components of the operation of the method were tested in natural conditions in various regions.

Example 1. On a pilot scale, the technology for softening produced water at the Bukinai field was tested. The initial formation water had the composition: (mg / l) Ca ²⁺ - 220-280; Mg ²⁺ - 93-130; Cl ^- - 730-800; SO ₄ ^2- - 780-920; NSO ₃ - 244-288; pH = 7.2-7.8. Precipitation of hardness salts was carried out for 8 months by adding ammonia (25%) to a solution of pH = 9.5. The resulting suspension was clarified in a cascade of three series-connected crystallizers with a volume of 2 m ³ each. The clarified solution containing <20 mg / l of calcium, again entered the reservoir through 8 injection wells. Well colmatation and a decrease in injectivity were not observed.

Example 2. On a pilot scale, a method for softening formation water of the same composition by adsorption on sulfonated coal was tested. The solution was filtered alternately in two filters of a factory design with a volume of 6 m ³ each. The residual calcium content in the filtrate did not exceed 15-20 mg / l.

As the cation exchanger was saturated, it underwent regeneration with a 10% sodium chloride solution. Throughout the entire period of testing the mudding of the wells and the reservoir during the injection of clarified solution was not observed.

Examples 3, 4, 5. At three fields in Kazakhstan, a gas saturator design was tested for mixing oxygen with a solution according to AC 1571828 on a pilot scale. Each test site included 8-10 injection wells. Oxygen in the wells came from cylinders connected to a common ramp.

During the test period, which lasted from 6 to 9 months, from the range of 26.7 tons to 32 tons of oxygen was supplied to the reservoir of each test site. Its concentration in the injection solution was in the range of 250-380 mg / L. The maximum specific consumption reached 0.47 kg / t of ore.

The efficiency of the extraction of precious metals from ores by thiosulfate-ammonia solutions has been repeatedly confirmed in laboratory conditions and on an industrial scale. The profitability of the PV method will depend on the degree of dispersion of the useful components, their content in ore, the oxidizability of the host rocks, the permeability of the formation and the magnitude of the hydrostatic pressure on the roof of the formation.

Claims (5)

1. The method of underground leaching of precious metals from ores of permeable alluvial and gold ore deposits, as well as weathering crust, including drilling a system of injection and pumping wells, injecting an oxidizing agent and a leaching solution into the ore-hosting formation, pumping out the productive solution, processing it by known methods of cementation, sorption, characterized the fact that ore mining is carried out in two stages: at the first, the ore-containing formation is oxidized with oxygen by flooding it with a softened working solution saturated with acid orodsoderzhaschim gas, wherein the pre-stored pressure solution clarified slurry from hardness salts and impurities, and in the second step was added to a solution of the exhaust Ammoniate copper thiosulfate, adjusted pH and the content of sulfite and sulfurous acid with ammonia, and this mixture is oxidized and leached noble metals. 2. The method according to claim 1, characterized in that for the softening of the formation solution, ammonia, hydroxides, carbonates, alkali metal hypochlorites, as well as ion-exchange materials: sulfonated coal and synthetic resins are used. 3. The method according to claim 1 or 2, characterized in that the pH of the softened injection solution is maintained in the range of 8.0-10.0. 4. The method according to claim 1, characterized in that process oxygen or oxygen-enriched air is used as an oxidizing agent during waterflooding. 5. The method according to claim 1, characterized in that the pH of the thiosulfate-ammonia solution is maintained in the range of 8.0-10.0.