RU2118991C1 - Method of undersurface leaching of gold at auriferous alluvials - Google Patents

Abstract

FIELD: gold-mining industry. SUBSTANCE: invention, in particular, relates to leaching fine gold in placers with nonuniform gold concentration distribution. Leaching is carried out in two steps: first, with potassium and/or magnesium chloride solution containing chlorine and having density exceeding that of formation water and, then, with chlorinated recycled solution. First-step salt solution is introduced into lower gravel level. Chlorinated solution is prepared either in flow-type electrolyzer or by chlorination of salt solution. Method gives rise to increased gold recovery, especially from lower gravel level and rock bed roof and also from argillaceous rock, permits treatment duration to be reduced, solution volume to be decreased, and prevents argillaceous rock swelling. EFFECT: enhanced process efficiency. 3 cl

Description

 The invention relates to hydrometallurgy and technology for the extraction of gold from ores at the place of their occurrence.

 It can be used by mining enterprises to develop alluvial deposits, characterized by a large specific share of fine and finely divided gold. The proposed non-cyanide method is most effective for leaching sand of relatively high thickness (> 2 m), characterized by uneven distribution of gold in thickness and characterized by the presence of poorly permeable clay inclusions, interlayers or clay rafts. In combination with the method according to RF patent N 2098619, 1997 it is environmentally friendly.

 Currently, alluvial deposits are mined exclusively by the traditional hydromechanized method with the gravity separation of the concentrate. This method is associated with the mechanical movement and processing of a large volume of ore, resulting in the formation of dumps that are subject to reclamation. In addition, the level of pollution by surface water slags increases and a significant proportion of fine and finely dispersed gold is lost.

 For example, according to the mining and geological characteristics of alluvial deposits of the Chita region, the share of non-recoverable fine gold (fractions -0.25 mm) exceeds 40%, the degree of mining of individual placers from the total reserves in the sands does not exceed 48%, and the design dilution of the sands reaches 30%. The costs associated with environmental protection and compensation for environmental damage reach 25-30% of the total cost of gold mining (Mining Journal, N 8, 1997, p. 33). The method of underground leaching of placer deposits is not practiced.

 There is a known cyanide method of underground leaching of frozen gold placers, which was tested in natural conditions (Mineev G.G. et al. Possibilities of gold mining by underground leaching of placers. - Novosibirsk: Nauka, 1979, analogue).

 When implementing it, problems arise associated with low leaching efficiency due to the lack of an oxidizing agent and the difficulty of feeding it into the formation, swelling of clay minerals, especially the montmorillonite group, in an alkaline environment, the safety of maintenance personnel, as well as unpredictable environmental consequences.

 There is a method of preventing the swelling of clay minerals during underground leaching of uranium, which consists in the fact that before pumping the carbonate leach solution into the ore-containing formation, the latter is pre-treated with a solution of potassium chloride (US patent N 4340253, 1982 - analogue).

 A well-known environmentally friendly two-stage method of underground leaching of gold and silver, including sequential extraction of gold first with an aqueous solution of chlorine and then silver with a solution of sodium thiosulfate (RF patent 2074958, 1994, prototype). The method is recommended for leaching the oxidized ores of weathering crusts, characterized by a relatively uniform distribution of useful components by the thickness of the ore-bearing formation. It has been successfully practiced by the mining company at the Gagar field since 1994.

 Alluvial deposits in many respects differ from weathering crusts. They are characterized by the presence of a lower waterproofing (raft), sometimes clayey, clayey layers and lenses, and, most importantly, the contrast of the power distribution of gold. The greatest enrichment, as well as an increase in the size of the gold particles, is observed in the lower interval of the sands, at the contact of the sands and the raft (at the junction) and in the roof of the raft itself.

 These characteristic geological and texture features of placers complicate their mining by underground leaching due to the possible under-extraction of gold from the enriched sand and raft intervals, as well as the swelling of clay layers and the raft surface under the influence of a salt leaching and working solution, especially containing sodium ions.

 The aim of the invention is to ensure effective leaching of the richest intervals of the reservoir, reducing the duration of mining, reducing the volume of the solution and preventing swelling of clay minerals.

 This is achieved by the fact that the placer is mined in two stages: at the first stage, a chlorinated solution of potassium chloride and / or magnesium having a density higher than the density of the formation water is fed into the formation, the solution being injected into the lower sand range, and the leaching of the entire chlorinated working solution to the second power of the productive horizon.

 The essence of the method lies in the fact that the development of the deposits begins from the lower interval of the sands and the roof of the raft due to the artificially created separation of saline and produced water. This delamination is expressed more sharply, the higher the concentration of salt in the injected solution. In addition, due to the increased concentration of chloride ion and hypochlorite in this interval, the most favorable conditions are created for the oxidation, complexation and transition of gold into solution. After stopping the supply of saline and the beginning of the stage of mining the entire productive horizon, the concentration of the circulating solution decreases due to dilution.

 The novelty of the method consists in the simultaneous use of three kinetic factors: ensuring the contact of the leaching solution with the most enriched placer interval at an increased concentration of oxidizing agent and complexing agent, as well as improving the interaction of the solvent with gold particles confined to the clay material by preventing its swelling.

 The usefulness of the method is determined by the absence of mechanical movement of the ore mass, the creation of conditions for the effective dissolution of particles of various sizes with a heterogeneous distribution of power and an increase in the degree of extraction of gold from total reserves.

 Practical implementation of the method is possible in all regions, including remote and permafrost zones. The main reagent - chlorine can be transported to the industrial deposits in a liquefied state in cylinders, barrels or obtained on site by electrolysis. Given the remoteness of the gold mining enterprise from transport routes, it is advisable to use autonomous mobile electrolysis plants of a modular type. In this case, the reagents consumed will be potassium, magnesium and sodium chlorides. For this purpose, all methods for producing chlorine can be considered, including diaphragm, with a mercury cathode or in flow electrolyzers with titanium-platinum, titanium-dioxide-ruthenium or titanium-dichroic manganese anodes. The most economical cells with a titanium dioxide-manganese anode. Electrolysis with a mercury cathode is less preferable for environmental reasons, but its advantages may appear in specific conditions.

 Example. The ore deposit is drilled by wells according to linear, square, hexagonal or other schemes. Wells are cased with production columns from polyethylene pipes of type PNP and equipped with filters. The injection wells in the first stage are additionally equipped with an inner pipe or a polyethylene hose for the entire length to the bottom. Pumping wells are equipped with airlift. The annulus of the wells above the filter is cemented.

 The processing complex includes an alkaline chlorine gas absorber, a sand trap, a sand and gravel filter, a sludge collector, a cementer, a coal sorption column, a saturated coal receiver, a salt solvent, an electrolyzer, a flow electrolyzer of the type KVU-2 or UV-0.5M and a current rectifier.

 When the power of the sand is about 2 m and above, the calculation of the flow rate of the saline supplied in the first stage is performed for an interval of about 0.2-0.3 m.

Thus, with a unit cell area of 400 m ^{2, the} amount of solution required for its salt flooding will be about 24 m ³ . When the productivity of the flowing electrolyzer is 2 m ³ / h, the duration of the water flooding will be 12 hours, and the consumption of potassium chloride at a concentration of 25 g / l in solution (d = 1.016 g / cm ³ at 10 ^o C) will be 0.6 tons.

 In the practice of preparing a saline solution containing chlorine in a flow electrolyzer, the concentration of chloride electrolyte can vary between 25-100 g / l, i.e., four-fold dilution is permissible during operation with a maximum concentration.

For electrolyzers with a titanium-dioxide-manganese anode, the current density is 1800-2000 A / m ² , and with a titanium-dioxide-ruthenium anode 4500-5000 A / m ² .

In this case, the chlorine yield by current reaches 85-88%, its concentration in the solution is 3 g / l, and the electrolyte temperature is 40-50 ^o C.

At the first stage of mining, the saline solution is fed to the bottom of the injection wells and pumped out from the pumped wells at the same rate. Then it is added with potassium chloride in a salt solvent and again served in a flow electrolyzer. Elevated temperature of the electrolyte (40-50 ^o C) increases the rate of dissolution of gold. The end of the first stage is fixed by the slip of active chlorine and obtaining a productive solution with a gold concentration of 0.5 mg / L. After this, the flow rate of pumping wells is increased. The concentration of chloride in the circulating solution decreases in proportion to the flow rate.

 At the development stage, the flow-through electrolyzer is turned off and the chlorination of the circulating solution is carried out with crude chlorine gas from the electrolytic cell with a solid cathode or liquefied imported gas.

 The chlorination mode is regulated by the value of the redox potential.

 Processing of the productive solution is carried out in two ways, depending on the concentration of gold in the solution: cementation on zinc powder or sorption on coal.

 The proposed method on the example of placer deposits of the Chita region will allow to increase the degree of gold recovery by 50-80% compared with the hydromechanical method due to the additional dissolution of fine gold, including from the most enriched interval of the productive horizon.

Claims (3)

 1. The method of underground leaching of gold from ores of placer deposits using chlorine, including drilling injection and pumping wells, feeding the leach solution into the reservoir, pumping and processing the productive solution by known methods, characterized in that the leaching is carried out in two stages: first, by supplying a chlorinated solution potassium chloride and / or magnesium with a density higher than the density of formation water, and the injection of saline solution is carried out in the lower interval of the sand, and then chlorinated a saline solution throughout the productive capacity of the horizon.  2. The method according to p. 1, characterized in that the electrolyte from the production of chlorine is used as a saline solution.  3. The method according to claim 1, characterized in that the concentration ratio of the sum of potassium and magnesium salts to sodium salt is maintained at least 2: 1.