RU2438790C1 - Method of preparing shungite rocks for dressing - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to complex processing and dressing of minerals and may be used for preparation of shungite rocks for dressing and extraction of noble metals (Au, Ag) therefrom. Proposed method comprises preliminary carbothermal reduction of shungite rock oxides by high-temperature silicon carbide synthesis at 1450°C in vacuum for 2 hours and annealing ceramic mix composed of 49 wt % of % SiC, 49 wt % of Al₂O₃ and 2 wt % of CaF₂ in atmosphere of argon at 1700°C for 2 hours and heating rate of 300 K/h/.

EFFECT: higher efficiency and expanded range of processed stock.

1 dwg, 5 tbl

Description

The invention relates to the integrated processing and enrichment of minerals and can be used to prepare schungite rocks for enrichment, namely to extract precious metals (Au, Ag) from them.

Shungite rocks are a carbon-containing mineral substance (with a carbon content of 5 to 90 wt.%). The carbonaceous substance contained in the ore forms a matrix in which quartz grains with a particle size of 0.5 μm are evenly distributed, less often mica, chlorite, albite, calcite and dolomite grains, as well as trace elements (Cu. Zn, Co, Ni, Cr , V, Mo, Pb, S, As, Se, Au, Ag, etc.). Mineral components, in particular noble metals, schungite rocks are characterized by a finely dispersed distribution in the form of crystals, layer (0.2-0.5 nm) interstitials and nanoclusters in shungite carbon. Therefore, obtaining industrial concentrates of precious metals (Au, Ag) from shungite rocks by mechanical methods or by chemical methods of hydrometallurgy is inefficient.

A known method of beneficiation of gold-quartz and gold-sulfide-quartz ores localized in black shale rocks (RU 2294800, B03B 7/00, 08/03/2005), including crushing ore in a jaw crusher, first screening, retreatment, second screening, classification of the under-sizing product in hydrocyclones, the third screening and centrifugal concentration, while the concentrates are combined for further cyanidation. The disadvantage is the complexity, duration and multi-stage process. And cyanidation is environmentally unsafe.

There is a method of processing refractory gold-bearing sulfide raw materials (RU 2025521, С22В 11/00, 03/13/1992), including preliminary desulphurization of the raw materials, then the resulting product is mixed with calcium and silicon-containing fluxes in effective quantities, then the mixture is melted, followed by cooling of the slag to its spontaneous spattering into powder and extraction of gold by known methods of enrichment. This method cannot be carried out on schungite rocks.

We have not identified ways to prepare schungite rocks for enrichment and to extract noble metals (Au, Ag) from them, which can be taken as a prototype.

The technical result of the present invention is to develop an effective method of preparing shungite rocks for enrichment and in expanding the raw material base to produce precious metals.

The technical result is achieved in that a method of preparing for the enrichment of noble metals of schungite rocks includes carbothermic reduction of schungite oxides in a vacuum furnace at a temperature of 1450 ° C, followed by heat treatment in an inert argon atmosphere at a temperature of 1700 ° C for 1-2 hours.

The method is as follows. The synthesis of β-SiC silicon carbide is preliminarily carried out: tablets are formed from powdered schungite, which are subjected to heat treatment at a temperature of 1450 ° C under vacuum for 2 hours

SiO ₂ + 3C → SiC + 2CO ↑

In addition to the β and α modifications of silicon carbide, free silicon (Si), quartz (SiO ₂ ) and an excess of carbon (C) are observed in the products.

Then, from a ceramic mixture of 49 wt.% SiC, 49 wt.% Al ₂ O ₃ and 2 wt.% CaF ₂ , tablets are formed which are fired in an argon atmosphere (P = 0.13-0.15 MPa) at T = 1700 ° C. for 2 hours and a heating rate of 300 K / h.

49 wt.% Alumina is introduced to compensate for the excess carbon, and 2 wt.% Calcium fluoride is used to intensify the metabolic processes in the system due to the formation of a liquid phase.

The interaction of shungite carbon with alumina leads to carbidization of Al ₂ O ₃ to monooxycarbide (Al ₂ OS)

Al ₂ O ₃ + 3C → Al ₂ OC + 2CO ↑

As a result, ceramics based on Al ₂ OC and SiC with fluid inclusions of complex compounds (Ag, Au, Cu, Hg, Si) (CF) are formed.

Further, during the cooling of the ceramic material (T = 300 ° C) and the reaction of carbon-fluorine-containing complex compounds with it, as well as the sorption of metals on Al ₂ OC grains, alloys are formed:

Al ₂ OC + SiC + (Ag, Au, Cu, Hg, Si) (CF) → (Si ₂ C ₂ ) _0.85 (Al ₂ OC) _0.15 + (Si ₂ C ₂ ) _0.65 (Al ₂ OC) _0.35 + alloys ( Au, Ag, Cu, Zn, Hg) ₂ (Al, Si, Fe) + F ₂ ↑ + СО ↑

Case Studies

The experiments on preparation for the enrichment of noble metals of schungite rocks were carried out on the rocks of the Zazhogino deposit (Republic of Karelia). During the research, a complex of mineralogical methods was used, including electron scanning microscopy, microprobe and x-ray phase analyzes. The chemical composition of the starting samples is shown in table 1.

Tablets were formed from powdered shungite, which were subjected to heat treatment at a temperature of 1450 ° C under vacuum for 2 hours. As a result of the total reaction, a cubic modification of silicon carbide is formed:

SiO ₂ + 3C → SiC + 2CO ↑

Further, tablets were formed from the ceramic mixture (samples 1.2, Table 2), which were fired in an argon atmosphere (P = 0.13-0.15 MPa) at T = 1700 ° C for 2 hours according to the scheme of the open reaction volume and heating rate 300 K / h The interaction of shungite carbon with alumina proceeds by the reaction:

Al ₂ O ₃ + 3C → Al ₂ OS + 2CO ↑

table 2 Arr. No. Source composition Enrichment conditions Phase Composition Mass loss,% 2% CaF ₂ Argon, 6H-SiC - 56.3% one 49% Al ₂ O ₃ T = 1700 ° C, 2 hours Al ₂ OC - 22.4% 46.4 49% SiC P reset Si - 21.3% 2% CaF ₂ Argon, 6H-SiC - 5.2% 49% Al ₂ O ₃ T = 1700 ° C, 2 hours 3C-SiC - 20.6% 59.4 2 49% SiC P = 0.13-0.15MPa Al ₂ OC - 60% Si - 14.2%

Further, in the process of cooling a ceramic material (sample 1) at T = 300 ° C and the reaction of carbon-fluorine-containing complex compounds with it, metal alloys containing a greater amount of gold, silver and other metals are released:

Al ₂ OC + SiC + (Ag, Au, Cu, Hg, Si) (CF) → (Si ₂ C ₂ ) _0.85 (Al ₂ OC) _0.15 + (Si ₂ C ₂ ) _0.65 (Al ₂ OC) _0.35 + alloys ( Au, Ag, Cu, Zn, Hg) ₂ (Al, Si, Fe) + F ₂ ↑ + CO ↑

According to X-ray diffraction and electron microscopy studies, each of the samples is a gray polycrystalline aggregate with particle sizes from 0.5 to 25 microns and a fairly high degree of surface disturbance. Microphotographs of the samples (see drawing) show rounded precipitations of a submicroscopic gold-bearing alloy.

When studying the microstructure of samples by scanning electron microscopy, a large number of grains are found in the samples, at some points of which the microprobe scanning shows the presence of nano- and microinclusions of gold (up to 69%), the size of these inclusions is up to 2 microns. The results of scanning electron microscopy of sample 1 are shown in table 3, sample 2 in table 4.

The interpretation of the diffraction patterns of samples 1 and 2 also confirms the presence of gold (Table 5).

Table 5 V.I. Mikheev. No. X-ray p / p determinant of minerals ", Sample 1 Sample 2 1957 Au Gold d, Å J _rel d, Å J _rel d, Å J _rel one 2.35 one hundred 2.34854 16 2.34229 5 2 2.03 90 2.03342 eleven 2.03585 5 3 1.437 80 1.43435 four 1.41690 3 four 1.226 90 1.22850 7 5 1.173 fifty

According to microprobe analysis, it was found that in associates the carbide phase- (Au, Ag) alloy noble metals are contained in approximately 1.5 g / t. Thus, for the first time, a technology has been developed for the enrichment of gold in the high-temperature processing of schungite rocks. The achieved concentration of noble metals (Au, Ag) allows the separation of valuable components by traditional methods (flotation, bromoformation, etc.).

Claims (1)

A method of preparing schungite rocks for enrichment involves preliminary carbothermal reduction of schungite rocks oxides by means of a high-temperature chemical process for the synthesis of silicon carbide at a temperature of 1450 ° C under vacuum for 2 hours and subsequent firing of a ceramic mixture of 49 wt.% SiC, 49 wt.% Al ₂ O ₃ and 2 wt.% CaF ₂ in an argon atmosphere at a temperature of 1700 ° C for 2 hours and a heating rate of 300 K / h.

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