RU2479650C1 - Extraction method of precious metals from ores and concentrates - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves processing of base material during heating in water vapour atmosphere and further leaching of precious metals from processing product in solutions of reagents. Besides, processing of base material is performed in water vapour atmosphere, which is mixed with oxygen at the temperature of 300-500°C at oxygen content in gas mixture within 10-20%. Waste gases released during the processing are brought into contact with the solution that is combined with a leaching solution.

EFFECT: decrease of temperature and reduction of costs at preparation of refractory ores and concentrates to leaching.

1 tbl, 1 ex

Description

The invention relates to the metallurgy of noble metals and, in particular, to methods for hydrometallurgical extraction of metals from technologically refractory raw materials, for example from carbonaceous ores and concentrates. The proposed method can be used in the analysis, as well as in the conduct of geochemical, geological prospecting and geological exploration, revaluation of balance and off-balance reserves in natural and man-made raw materials.

The vast majority of types of mineral raw materials of precious metals consists of crystalline and amorphous inorganic and organic components. In favorable cases, the noble metals can be in the raw matrix in the form of discrete metal particles or interspersed in the structure of certain carrier minerals. Such raw materials do not present technological difficulties for industry and analysis.

In many types of ores and concentrates, gold and platinum metals are in the form of individual nuclei, subatomic size of clusters and clusters, which are chemically or physically associated with the surrounding condensed inorganic and organic matter of the matrix. With such scattering, the extraction of any elements from the matrix of raw materials is an extremely difficult task. For example, technologically resistant types of gold-bearing raw materials include granites, clays, metamorphic schists, gneisses, in particular carbon-containing, black sands, graphite and many others. In these rocks, especially carbon-containing, significant amounts of noble metals scattered in the matrix can be found. They are poorly recoverable by processing with traditional cyanidation methods. Numerous publications emphasize that the organic compounds of gold and platinum do not dissolve in cyanide solutions and remain in the leach tailings.

The most common methods for processing refractory ores and concentrates include preliminary physical disintegration by dry or wet processes to technically and economically justified particle sizes of at least 0.1-0.01 mm. This operation allows you to partially expose the inclusion of precious metals that are in the matrix in the form of native or intermetallic particles having a size of at least 0.001 mm. Smaller gold particles can be separated from the matrix of raw materials and extracted in the next step into the reaction solution only after further chemical disintegration of the refractory particles of the matrix of raw materials. For this purpose, stubborn raw materials after physical grinding are subjected to thermochemical, chemical or more complex processing. For example, refractory raw materials are subjected to oxidative roasting at 500-1000 ° C followed by leaching of noble metals from a cinder ([1] Maslenitsky IN, Chugaev LG Metallurgy of noble metals. - M .: Metallurgy, 1987. - 366 p. .). A type of preparation of concentrates for cyanidation is firing in the presence of lime or other calcium-containing materials ([2] RF Patent No. 2078146 of 04/27/1997), which solves the problem of utilizing sulfur dioxide.

In these methods, the unproductive components of the matrix of raw materials are destroyed, and the noble metals are transferred into a solution, concentrated and then a commodity product is isolated from them by known methods.

None of the known methods of industrial (non-laboratory) chemical treatment with reagents can achieve the required completeness of opening the resistant part of the matrix of raw materials or its sufficient permeability for oxidizing agents, complexing agents or extractants, which could ensure the maximum extraction of rare metals. In this regard, a significant part of valuable metals is irretrievably lost with leaching tails, which leads to a decrease in economic and environmental production efficiency. The most radical approach is the melting of refractory concentrates into lead, copper or other alloys, followed by the separation of noble metals from it by known methods [1].

Pyrometallurgical processing of refractory raw materials, including oxidative roasting or smelting in order to collect noble metals with copper, lead or other metals is inevitably accompanied by the loss of micron particles of gold and platinoids with dust and gaseous products.

The closest in technical essence and the achieved effect is a method of processing gold-bearing ores and concentrates (RF Patent No. 2309187 from 10.27.2007), including firing in an atmosphere of water vapor at a temperature in the furnace of 700-900 ° C. Pre-ground raw materials are placed in an oven and heated in a steam atmosphere. Under these conditions, the raw material matrix is destroyed, in particular, sulfur and arsenic pass into the gas phase, and microparticles of precious metals are fully opened for further cyanidation. If the feedstock contains organic carbon, then, as practice shows, it also decomposes in a vapor atmosphere. The steam treatment product is leached in reagent solutions. In particular, the leaching of the calcination product in cyanide solutions proceeds without complications.

At the same time, the gaseous products of this reaction and sulphurous gases entrain the released microparticles of precious metals and remove them from the cinder. Subsequent recovery of gold from the sulfur-containing gas products and dusts significantly complicates the process.

The basis of the invention is the task of simplifying the preparation of refractory concentrates, primarily carbonaceous, for cyanide leaching while eliminating the loss of precious metals. In particular, the goal is to reduce the temperature and associated costs when processing raw materials with steam.

The specified technical result is achieved in that the concentrates are fired in an atmosphere of water vapor and oxygen at a temperature of 300-500 ° C, and the oxygen content in the initial gas mixture is maintained within 10-20%, and the exhaust gases are brought into contact with the solution that is used when leaching.

The basis of the proposed method is the chemical-thermal destruction of the organic matrix, as part of carbonaceous ores and concentrates of precious metals, to increase the efficiency of subsequent leaching.

The process according to the method of the prototype at temperatures above 700 ° C also allows you to destroy organic structures, but in such conditions the oxidation of sulfide sulfur occurs, accompanied by the release of large volumes of sulfur dioxide and arsenic; oxides of iron and non-ferrous metals are formed. Both circumstances negatively affect the technical and economic indicators of the process: the costs of steam overheating, gas utilization and purification are high, and noble metal particles are screened to one degree or another by passivating films - recovery during cyanidation is reduced.

It is well known that the mineral forms of carbon and organic compounds, primarily graphite, are very stable in air. In an atmosphere of water vapor without oxygen, the oxidation of carbon by reaction

according to thermodynamic calculations starts at 650 ° C.

Thermodynamic calculations showed that in the presence of oxygen, carbon oxidation

should flow over the entire temperature range. The results of the experiments established that the oxidation of carbonaceous substances in the composition of gold-containing concentrates in the atmosphere of water vapor and air begins at a temperature of 250-270 ° C. An organic decomposition rate acceptable for the practical application of this method is achieved at temperatures above 300 ° C. It is noteworthy that with the combined action of steam and oxygen in the air, the oxidation of sulfides begins to develop only from 600 ° C.

The oxidation rate of organic substances is significantly affected by the oxygen content in the initial gas mixture. In devices (steam generators) used in practice, steam is obtained by evaporating water in closed and sealed containers. In order to save energy during subsequent overheating and maintaining a high temperature, steam seeks to prevent its dilution with air. In practice, the content of free oxygen in the gas mixture supplied to the processing of concentrates due to the "suction" of air can be 1-2%. As experience has shown, at temperatures from 300 to 600 ° C, such an amount of oxygen is not enough to activate the process by reaction (2). And only with an oxygen content of 10-12% in the indicated temperature range, intense oxidation and decomposition of carbonaceous substances of mineral concentrates is observed. Processing carbonaceous concentrates at a temperature of more than 600 ° C does not give an additional effect, and if sulfides are present in the processed raw materials, intensive oxidation of sulfides begins, which is not always justified. Greater than 20%, the oxygen content in the initial mixture also does not give a positive effect. In this regard, the optimal composition of the gas mixture is atmospheric air, diluted 1.5-2 times in volume with steam.

As a result of the oxidation of organic carbon, metal gold particles are released for subsequent leaching. It was found that the organic compounds of gold are destroyed in this case, gold is restored to a metallic state, i.e. goes into cyanide form.

At the same time, the gold microparticles present in the raw material initially and formed during the decomposition of organics (“pulverized” gold) can be entrained from the reactor by the outgoing steam-gas mixture during steam treatment. Steam in this system is a good gold extractor that does not allow it to settle on the walls of the duct. To capture particles of noble metals, it is advisable to bring the vapor-gas mixture into contact with water or with special trapping solutions, for example, bubbling. A similar approach is proposed for trapping gold from flue gases generated during coal combustion (RF Patent No. 2249054 of 03/27/2005). In this method, technical circulating solutions used for leaching gold from steam treatment products of concentrates can be used as trapping gold. In this case, noble metals pass into the solution and are further extracted by known methods in the main technology.

The implementation of the proposed method is discussed in the following examples.

The initial gold-containing sulfide (pyrite) concentrate contained 37 g / t of gold, 85 g / t of silver, 43% sulfide sulfur and 1.1% organic carbon. Carbon in accordance with the data of IR spectroscopy was represented by bitumen and organomineral forms. In terms of the combination of properties exhibited by the concentrate in cyanidation processes, it can be classified as resistant. Direct cyanidation of the concentrate makes it possible to extract gold by no more than 47% and silver by 29%.

Samples of a gold-containing carbonaceous concentrate weighing 200 g each for the purpose of thermochemical opening of gold before cyanidation were subjected to treatment in a stream of superheated steam in a laboratory setup. For this, the concentrate was placed on a porous septum in a vertically arranged tube furnace with an electric heater. Heating to a predetermined temperature was carried out with control using a chromo-aluminum thermocouple, the junction of which was placed directly into the volume of the concentrate. Automatic temperature control was carried out by a microprocessor single-channel meter-controller TPM1 according to the PI law.

The source of steam was a sealed container of water, heated to a boiling point and connected to a steam treatment reactor. Steam from bottom to top passed through a layer of concentrate and through a hot pipeline entered a container with a trapping solution. Excessive steam pressure in the working area corresponded to the depth of immersion of the exhaust pipe into the capture solution and amounted to 0.005 MPa. Steam consumption and processing time (1 hour) were the same in all experiments.

To introduce oxygen into the initial mixture, air was supplied directly to the steam-heating part of the furnace (in experiments 4 and 5, an oxygen-air mixture). The oxygen content in the vapor-air mixture in contact with the sample was calculated taking into account the flow rates of steam, air, the indicated pressure in the reaction zone, and the set temperature according to known dependencies.

After steam treatment and cooling of the sample, the concentrate was leached in a reactor with a pneumomechanical mixer (laboratory flotation machine) in a cyanide solution (1 g / l NaCN, pH 10.3, W: T = 2: 1, duration 24 hours). After leaching, the pulp was filtered, the cake was washed, and the content of gold and silver in the solution and in the solid residue was determined. Based on the numbers obtained, gold recovery was calculated.

Experiment 6 was conducted according to the conditions of the prototype: only steam was fed into the furnace and the sample was heated to 750 ° C

Vapor trapping solutions were analyzed for gold. In experiment 7, for the preparation of the leach solution, the solution obtained by trapping steam at the stage of steam treatment of the initial sample was used. The results of the experiments are presented in table 1. The solutions obtained by trapping the vapors by the method of the prototype had an acidic character due to the formation of sulfur and sulfuric acid in them. Such solutions cannot be used for the preparation of a leaching cyanide solution. Extraction of gold from them requires an independent technology.

Table 1 The results of the experiments Experience number Steam processing temperature, ° C The oxygen content in the mixture,% Recovery in solution,% Loss of gold with tails,% Gold recovered in a capture solution,% Au Ag Au Au one 250 5 58 37 42 0 2 300 10 79 64 19 2 3 400 fifteen 85 69 13 2 four 500 twenty 87 72 10 3 5 600 25 85 71 9 6 6 prototype 750 Did not expect 80 73 12 8 Sour solution 7 450 fifteen 83 71 13 2

Comparative analysis of well-known technical solutions, including the method selected as a prototype, and the present invention, allows us to conclude that it is the totality of the claimed features ensures the achievement of the perceived technical result. The implementation of the proposed technical solution makes it possible to increase the extraction of gold from carbonaceous concentrates in commodity solutions by 3-5% and reduce the cost of processing concentrates.

Claims (1)

A method of extracting precious metals from ores and concentrates, including processing the starting material when heated in an atmosphere of water vapor and subsequent leaching of precious metals from the product in the reagent solutions, characterized in that the processing of the starting material is carried out in an atmosphere of water vapor mixed with oxygen at a temperature of 300 -500 ° C, and the oxygen content in the gas mixture is maintained within 10-20%, and the exhaust gases from the treatment are brought into contact with the solution, which is combined with the solution leached Chiwan.