Precious metals, namely gold Au, silver Ag, platinum Pt, palladium Pd, strontium Sr, osmium Os, rhodium Rh and ruthenium Ru eight metals. Due to the scarce content of these metals in the earth's crust, difficult to extract, but excellent performance, widely used, expensive and named precious metals. In addition to the familiar gold Au, silver Ag, the other six metal elements called platinum group elements (platinum group metals).
The abundance of precious metals in the earth's crust is extremely low, in addition to silver deposits of higher grade, more than 50% of the gold and more than 90% of the platinum group metals are dispersed *** born in copper, lead, zinc and nickel and other heavy non-ferrous metal sulfide ores, their content is very small, grade low to PPm level or even lower.
With the development of human society, the application of mineral raw materials is expanding, the human demand for minerals is also increasing, therefore, the need to maximize the utilization of mineral resources and metal recycling rate. Due to the high chemical stability of precious metals, for their regeneration and recycling to provide the conditions, coupled with its own rare, regenerative recycling profitable.
Second, the precious metal recycling profile
As precious metals in the use of the process itself is not loss, and in the parts of the content than the original ore to be much higher, the countries containing precious metal waste as rare precious metal raw materials, and to give sufficient attention. And have to legislation, and the establishment of professional precious metal recovery company.
Japan in the 1970s on the enactment of solid waste disposal and removal of laws, the establishment of recycling associations, to date, has been recovered from the precious metal-containing waste in the recovery of valuable metals more than 20 kinds.
The United States recovery of precious metals has been decades of history, the formation of recycling industry, the establishment of specialized companies, such as Amex Metals and Engelhardt, in 1985 on the recovery of 5 tons of platinum group metals, in 1995, the recovery of precious metals increased to 12.4 ~ 15.5 tons.
Germany enacted the Waste Management Act in 1972, which stipulates that waste must be recycled as raw materials, and requires the improvement of the degree of environmental harmlessness of waste. Germany has a famous Digosha and dark packet rock raw materials company have built a special device recycling treatment of waste containing precious metals.
The United Kingdom has a global metal recycling company - Amalon Metals, specializing in the recycling of all kinds of waste containing precious metals, the recovery of platinum, palladium, silver enrichment of thousands of tons.
China's various types of electronic equipment, instruments, electronic components and household appliances, etc. With the economic development and the improvement of living standards, the elimination rate is rapidly increasing, the formation of a large number of waste waste, not only a waste of resources and energy, and cause serious environmental impact. With the continuation of time, the number of updates will increase. If buried or burned as municipal waste, it will cause serious pollution of air, soil and water, affecting people's health. And electrical equipment contacts and solder joints contain precious metals, should try to recycle and reuse.
Third, the production process
According to the raw materials, scale, product program, the recovery process is different. In general, for copper, lead anode sludge fire and wet method of difference, for secondary resources in addition to fire wet method also involves dismantling, mechanical and pretreatment processes.
1, copper anode sludge treatment process
l Pyro process
The traditional pyro process is as follows
Copper anode sludge
H2SO4 sulfuric acid roasting Flue gas (SO2 SeO2) Absorption
Dilute H2SO leaching CuSO4 solution Crude Se
Leach slag
Reduction melting Slag
Reduction Smelting Slag
Precious Lead
NaNO3 Oxidation Refining Dross Recovery Bi Te
Silver Anode
Silver Electrolysis Sponge Silver Ingot
Black Gold Powder
Gold Electrolysis Waste Electrolyte Recovery of Platinum, Palladium
Gold Plate Gold Ingot
The main part of the process is the separation of the sulfated roasting leaching. Copper into soluble copper sulfate, selenide decomposition of selenium oxidation for selenium dioxide volatile separation, containing SeO2 and SO2 gas pumped by the gas pipe to the absorption tower, SeO2 is absorbed by the water to generate H2SeO3, and at the same time in the water SO2 is reduced to crude Se. roasting and leaching of CuSO4 and part of the AgSO4 telluric acid sulfuric acid solution, with the replacement of the copper (flake or powder) containing tellurium crude silver powder sent to the silver refining. The copper (flakes or powder) is used to replace the tellurium-containing crude silver powder and sent to silver refining. Gold and silver are enriched in the leaching slag. Reduction smelting mainly with leaching slag plus lead oxide or lead anode mud merger, the output of precious lead containing gold and silver, and then precious lead by oxidation refining separation of lead, bismuth and tellurium, cast for gold and silver alloys, by silver electrolysis and refining, the output of sponge silver ingots, silver sludge (black gold powder) electrolysis gold, gold electrolysis waste recovery of platinum, palladium. The method is characterized by a high recovery rate of up to 90% or more, the adaptability of raw materials, more suitable for large-scale processing, Europe and the United States and the former Soviet Union countries are mostly used in the fire process, the disadvantages of the process is redundant, more intermediate links, backlog of metal and capital serious, especially when the scale is more prominent, affecting economic efficiency. In addition, high-temperature incineration produces harmful gases, especially the volatilization of lead, producing secondary pollution, so its application is limited.
● Wet process
In the 1970s, the wet process rose rapidly and was recognized by the domestic metallurgical community, the following is a brief introduction:
Copper anode mud
H2SO4 leaching copper CuSO4 solution
Acetic acid leaching lead Cu, Pb solution
HNO3 leaching silver AgNO3 solution Ag
Aqua regia leaching gold Slag Smelting Recovery of Sn
Gold solution
Extraction and refining
Gold powder
The method uses different acids to leach base metal impurities in anode sludge in segments to enrich gold and silver. With H2SO4 first copper becomes CuSO4, leaching lead with acetate at room temperature, so that the lead generates soluble lead acetate (Pb(Ac)2) separation. Leaching slag with nitric acid to dissolve silver, copper, selenium, tellurium, silver-containing solution with hydrochloric acid or salt precipitation out of silver chloride (AgCl), the purity of which can reach more than 99%, the recovery rate of up to 96%, and then from the silver chloride in the extraction of silver refining, using aqua regia to dissolve the gold from the slag of nitric acid lithophosphoric acid, the gold solution with dibutylcarbinol (DBC) extraction, oxalic acid direct reduction of the gold products, the purity of the gold & gt; 99.5%, recovery rate Recovery rate can reach 99%. The total recovery of gold and silver in wet process is more than 99% and 98% respectively. Because the whole process of metal separation are in acidic aqueous solution, so it is called the whole wet process, compared with the fire process, there is low energy consumption, good utilization of valuable metals, less waste, the production process is continuous and other advantages.
l Processing and metallurgy combined process;
Copper anode mud
H2SO4 milling de-copperization
Leaching CuSO4 solution
Leaching slag
H2O adjusting slurry
Flotation tailings lead refining
Concentrate
Firing roasting roasting flue gas recovery of selenium
Silver anodes Electrolysis Silver Powder Silver Ingot
Black Gold Powder Electrolysis Gold Plate Gold Ingot
This process is used to process copper anode sludge with high lead content, the process includes anode sludge plus sulfuric acid grinding and leaching copper, leaching slag containing gold and silver slurry adjustment for flotation, the selected concentrates are melted for soda oxidation to produce silver anode, and the electrolysis produces silver and gold powder. The recovery of gold and silver in the process reaches 95% and 94% respectively. Due to the introduction of flotation process, the size of concentrate smelting equipment for the fire process 1/5, reagent consumption savings of half, reduce lead pollution, simplify the subsequent smelting process, improve economic efficiency.
l Tianjin Datong Copper Co., Ltd. gold and silver plant anode sludge treatment process
Ingredients
Cu Au Ag Pb Sb Bi Sn Ni As Te
15.64 2132g / T 15.94 9.95 20.17 1.32 0.92 0.40 7.30
Process
Anode mud
H2SO NaClO3 (oxidizer)
Dilute acid leaching
Controlled potential V420mv
Slag Furnace slag
HCl H2SO4 NaClO3
Controlled electrochemical chlorination of V.1200mv gold Sedimentation of Se Te
SO2 Cu powder substitution
p> SO2 SeO2 solution
Furnace liquid NaClO3 slag 1200mv Recovery of H2SeO3
Crude Te CuSO4
Tail Liquid Au Powder Selenium
Oxalic Acid Secondary Gold Controlled Chlorination Concentration Crystallization Tail Liquid
Furnace Liquid Slag
Au Powder Tail Liquid Sodium Thiosulphate Leaching Silver
Au ingot casting
Slag slag
Enrichment of Pb.Sb water with hydrazine precipitated silver
Export
Tail liquid silver powder
Silver powder
Silver anode mud
Electrolysis
Electro-silver anode mud Electrolyte
Recycling of gold
The design of this process does not have a pre-bake process, but by adding oxidizing agent during copper leaching. The process is designed without pre-burning process, but to add oxidizing agent (NaClO3) when leaching copper, so that the Cu, Se, Te in the anode mud oxidized into CuSO4, H2SeO3 and H2TeO3 and transferred to the solution, in the solution of H2SeO3 with SO2 reduction to get the crude Se, Te is replaced with copper powder to get the Te concentrates, the CuSO4 through the concentration of the crystalline CuSO4.5H2O. the leach residue through the secondary control of electricity Chlorination of gold leaching, the primary leaching of gold with SO2 reduction, the secondary leaching of gold with oxalic acid reduction, gold recovery up to 98.4%, controlled chlorination of slag with sodium thiosulfate (Na2S2O3) leaching silver. Sodium thiosulfate reagent toxicity is small, less consumption, fast reaction speed, suitable for dealing with silver-containing materials, silver recovery rate of up to 99%, purity of 99%.
The anode mud of Chase Copper Co., Ltd. contains more lead and antimony than general copper anode mud, similar to lead anode mud, so the process used is similar to the chlorination process of lead anode mud, first of all, the copper, arsenic, antimony, bismuth, and some of the lead in the lead anode mud is leached with FeCl3 or HCl + NaCl solution, and at the same time, there is a small portion of silver to generate AgCl2- dissolved, and the leachate is diluted with water to PH0.5, so that SbCl3 hydrolyzed to SbOCl precipitation, while precipitating AgCl (precipitation rate of 99% or more), leaching slag with ammonia solution to leach silver, so that the conversion to soluble Ag (NH3) 2Cl, and then from the solution with hydrazine hydrate reduction of silver, ammonia leaching slag with HCl + Cl2 or HCl + NaClO3 leaching recovery of gold, the difference lies in the choice of the gold, silver recovery successive Problems, which need to depend on the specific composition.
The above are several typical principle processes to deal with various kinds of anode sludge, and different combinations can be carried out according to the composition of anode sludge to be dealt with.
2. Recovery process of gold, silver-based alloys and bimetallic composites as well as precious metal spent catalysts with carriers.
● Recovery process of gold and silver alloys and metal scrap waste and scrap
Bimetallic scrap waste containing Au, Ag, and ΣPt
Pre-treatment
Thermal decomposition at 400~600℃
Nitric acid leaching
Insoluble residue (Au, Pt, Pb, etc.) Nitric acid leaching solution (containing Ag and other metals)
Cl
Dissolution Recovery of AgCl
Residue Solution AgCl Other Metals
Sulfide SO2 or NaSO3
Sinking of gold Crude Ag purification
Crude Au solution (Pt, Pb)
Purification
Pretreatment can be dismantling or mechanical treatment, thermal treatment of the The main purpose is to remove organic matter at 400 ~ 600 ℃, as well as low-soluble metals, and then dissolved with qN HNO3, so that the material in the oxidation of silver and other base metals, in the form of nitrate transferred to the solution, from the solution to recover silver and purification, nitric acid insoluble residue, you can use aqua regia or aqueous chlorination to leach or other dissolution of gold, platinum and palladium, recovered from solution to separate and purify Au, Pt and Pd. < /p>
Gold solution (Pt, Pb), gold, Pb and Pd, gold, Pb and Pd. /p>
Gold purification: crude gold back to dissolve the gold with dibutyl alcohol extraction, after the counter-extraction, and then sinking gold, get purified. And containing Pt, Pd solution can be used in dialkyl sulfide or N-second chapter of amino acetic acid (N540) extraction of palladium, to achieve the separation of platinum, palladium extraction rate of up to 99.5%, the platinum extraction rate is almost zero. The organic phase is washed with water and the palladium is counter-extracted with NH3.H2O, and the counter-extracted solution is then recycled to purify the palladium. Dialkyl sulfide is considered to be by far the most effective extractant for industrial separation of platinum and palladium, and its only drawback is that it is slightly less stable, easy to oxidize, and the extraction equilibrium time is a little longer, and the extract is recycled platinum. Of course, you can also use 30% N540 isoamyl alcohol + 70% kerosene extraction platinum and palladium separation. 30% N540 extraction of platinum conditions 4-stage extraction, 1-stage washing 3-stage counter-extraction, platinum extraction rate of up to 99.9%, 4NHCl counter-extraction, the counter-extraction rate of 99.95% from the counter-extracted solution to obtain the purity of 99.9% of platinum products.
For platinum, palladium separation and purification issues, the traditional method is repeated precipitation method, hydrolysis precipitation method, sulfide precipitation, ammonia salt precipitation or ion exchange separation. The disadvantages of precipitation method, firstly, the separation efficiency is not high, secondly, the cycle is long, low recovery rate, reagent consumption, poor operating conditions trouble. Ion exchange method, resin saturation concentration is low, the dosage is large, the exchange is thorough, exchange time is long. Extraction separation extraction is the recent rise of the separation method, it spreads fast, avoiding the most complicated liquid-solid separation in hydrometallurgy, the extractant can be recycled, the process is relatively simple, the cycle is short, the metal recovery rate is high, the purification effect is good. Therefore, it is widely used.
● ∑Pt as the carrier of the catalyst recycling process
∑Pt carrier has a honeycomb and small spherical high solubility silica, alumina, due to the high temperature process of use of some of the precious metals will be penetrated into the inner layer, some of them are sintered or glazed wrapped, or transformed into chemically inert oxides and sulfides, so their recycling carries a certain degree of difficulty. Their recovery must be enriched by the pretreatment stage, and then separation and purification, pretreatment enrichment stage is divided into:
▲ Fire enrichment method, high temperature smelting with iron as an auxiliary collector. Carbon as a reducing agent, plus carbon flux to make the carrier into a low melting point, low viscosity slag, to obtain a platinum group metal-rich ferroalloys, followed by acid leaching to remove iron, to obtain platinum group metal concentrates. The Pd, Pt recovery of this method is 99%, 98% or more, respectively. Can also use sulfide (Fe2S, Ni3S2) as a trapping agent, lower temperature smelting, to obtain ice nickel after the aluminum live method of acid leaching, to obtain the platinum group metals concentrate.
▲Carrier dissolution method: γ-Al2O3 carrier catalyst, after grinding fine with H2SO4.NaOH or NaOH + Na2SO3 + biamine solution to directly dissolve alumina, and precious metals are all enriched in the insoluble slag.
▲And then the subsequent separation and purification can be connected to the wet part of the above process to form a complete process.