There are two types of silver extraction: wet and fire.
(1) Wet method
Wet method of silver extraction has cyanidation, sulfuric acid leaching, slurry electrolysis and other methods.
1. Cyanidation method (non-toxic agents are also available)
Is simple and widely used method, the concentrate or ore flotation process directly, metal silver cyanide reaction:
Ag+O2+8CN-+2H2O=====4Ag(CN)2-+4OH-
The angle silver ore (AgCl) and the silver ore (Ag2S) in the ore are also cyanated according to the following reaction.
AgCl+2CN-=====Ag(CN)2-+Cl-
Ag2S+4CN-+2O2=====2Ag(CN)2-+SO42-
However, the silver cyanide has a slow cyanidation rate and consumes more cyanide agents, which requires strong aeration.
The cyanidation process is similar to the requirements of the ore properties and composition, and the cyanidation conditions are similar to the gold cyanidation method. Arsenic , antimony and sulfur are harmful. The noble liquid produced by cyanidation (containing 0.2-1 g/L of silver) is generally extracted by zinc or electrowinning. For example, the Popian Silver Mine in South Korea (age grade 165g/t), Shilipu Silver Mine (ore grade 280-450g/t) in Shandong, China, the silver grade of flotation concentrate increased to 0.9% and 0.6%-l.1 respectively. %, flotation and cyanidation recovery rates were 92% and 98%, respectively, with a total yield of 90%. Hundreds of small silver mines in the western United States are treated by heap leaching, such as silver grade 152g/t. Silver minerals are mainly ore of horn silver mines. After crushing to -9.5mm, each ton of ore is accompanied by 0.45-0.9kg of cement, 4.5. Kg lime, wetted with 0.1% sodium cyanide solution, piled up, sprayed with cyanide solution, replaced with zinc in noble liquid, smelted into anodic electrolysis to obtain pure silver. When the flotation concentrate containing copper, arsenic, antimony higher pretreatment required removal arsenic, antimony. For example, the Equudi gold ore flotation concentrate in Canada contains (%): Ag6.8, Cu 17.2, Sb 4.1, As 4.1, first steamed with a NaHS solution (sodium sulfide dissolved in water) in a stainless steel tank. Section leaching (16h + 8h), the leachate closed loop. The filtrate is first evaporated to crystallize sodium citrate [NaSb (OH) 6], and the filtrate is then boiled with lime (pressure about 600 kPa, temperature about 190 ° C) to produce calcium arsenate Ca3 (AsO4) 2, which is beneficial to profit. The leaching residue is recovered by cyanidation or other methods to recover silver, copper and gold.
2. Mixed acid leaching
When the ore silver grade is higher, the silver can be directly leached with sulfuric acid-nitric acid mixed acid, such as the small silver mine distributed in northern Canada. One of the silver ore contains about 1000g/t of silver, and the silver is up to 30 by re-election (jigging). %-37% of the re-elected silver concentrate is then treated by flotation to obtain 2%-4% of the flocculated concentrate containing silver. Both concentrates can be leached with sulfuric acid and nitric acid mixed acid to extract most of the symbiotic metals except for lead in the silver and ore. The leaching solution precipitates AgCl with HCl or NH4Cl, and then converts silver chloride to Ag2S with (NH4)2S. Nitric acid and sulfuric acid were oxidized to silver sulfate in an autoclave, and then ammonia was combined into [Ag2(NH3)2SO4", and hydrogen was reduced to pure silver in another autoclave. The solution after separating silver chloride recovers nickel , cobalt and copper, and the recovery rate of valuable metals is more than 98%, and it is also possible to produce fertilizers (NH4)2SO4 and NH4NO3 by-product.
3. Slurry electrolysis
This is a method invented in China for the treatment of flotation concentrates from polymetallic symbiotic ore. For flotation concentrates containing Pb 5%-10%, Cu 3%-5%, S 36%, Ag 250g/t, Au 40g/t, firstly use sodium chloride solution and concentrate to form slurry, in machinery A DC electric field is applied to the stirred electrolytic cell to dissolve lead and silver (dissolution rate 97%-99%) and part of copper, and the process power consumption is 120-250 kWh/t. Cathode powder mainly containing lead (containing 70% lead) and containing copper (3%-12%) and silver (0.1%-0.15%) is deposited from the cathode, lead powder is fused by lead anodic electrolysis, and silver is recovered from the anode slime. . Leaching slag (containing Pb 0.3%, Cu 3%-4%, Au 60g/t) is extracted by cyanide dissolution-carbon adsorption-desorption-electrowinning method, the cyanidation rate is 96%-98%, adsorption rate, desorption rate The direct yield of each segment of the electrowinning is greater than 99.6%. The cyanide slag was isolated and floated out of copper concentrate (yield 10%, containing 18% Cu, Ag 400 g/t, Au 10 g/t) and sulfur concentrate (yield 55%, containing S50%). The total recovery rate of the whole process is: Pb 96%, Cu 94%, S90%, Au 95, Ag 96%. Achieve comprehensive and comprehensive utilization.
(2) Fire smelting
When silver-containing lead or copper flotation concentrate is fired and smelted, the silver and gold are quantitatively enriched in the smelting product - crude lead or copper bismuth (also known as "copper ice copper").
There are more than ten kinds of metals in the crude lead. The recovery route of silver and gold is determined by the crude lead refining method. The traditional pyrometallurgical refining firstly converts copper into copper sulfide scum separation, and then uses air oxidation or alkali to convert tin , arsenic, antimony, etc. into oxides or arsenic, citrate scum separation, and then to 450- The molten zinc solution was added to the molten lead liquid at 510 ° C to stir, and a silver-zinc alloy (silver-zinc shell) having a relatively high melting point was precipitated and floated on the surface of the lead liquid. The enrichment can be returned to the new material to increase the grade of silver, and the mechanically entrained lead in the silver-zinc alloy removed can be separated by a press. The silver-containing materials produced (generally containing Ag 10%-20%, the balance being lead and zinc) are first distilled and sealed in a closed distillation tank at 1100-1200 ° C to recover zinc. The lead liquid containing silver is at 883 ° C ( The melting point of lead oxide is oxidized above the air to separate lead and antimony from liquid lead oxide and high-density silver-gold alloy. The method processes the lead concentrate with high silver content, the process and the processing cycle are short, the equipment is easy to solve, and has certain advantages. However, the environmental pollution is serious, the reprocessing of various intermediate products is complicated, and the valuable metals are more dispersed. Nowadays, most smelters are cast into crude lead anodic electrolysis after removing copper from crude lead, and recover silver, gold and other valuable metals from electrolytic anode mud.
The copper bismuth treatment process is relatively simple. The molten copper enamel is blown in the converter with air or oxygen-enriched air to convert the copper sulphide into blister copper. The gold and silver in the sputum are trapped in the blister copper, and the blister copper is cast into Anode electrolytic refining, gold and silver are concentrated in copper anode mud, from which silver, gold and other valuable metals are recovered.
There are several treatment methods for zinc concentrate: high temperature oxidizing roasting of volatile zinc oxide and lead oxide in rotary kiln; or low temperature roasting, using flat tank, vertical tank, electric furnace or blast furnace to reduce zinc oxide to zinc vapor to be condensed into crude zinc; or after roasting Dissolved in sulfuric acid as zinc sulfate. Either way, silver remains in the slag and can range from tens to hundreds of grams per ton.
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