Lead refining method

First, the smelting method

Lead- smelting raw materials are mainly lead sulfide concentrates and a small amount of lump ore. Lead smelting methods include fire method and wet method. At present, the world is dominated by fire method, and wet method lead is still in the experimental research stage. The pyrometallurgical lead is basically a sintering roasting-blast furnace smelting process, accounting for 85% to 90% of the total lead production; followed by a reaction smelting method, which can be used in a kiln furnace, a short kiln, an electric furnace or a vortex furnace; use. The refining of lead is mainly carried out by fire refining, followed by electrolytic refining, but in China, electrolysis is not widely used due to customary reasons.

Refining raw materials are mainly of zinc sulfide concentrates of zinc oxide and a small amount of product. Zinc pyrometallurgical distillation uses vertical tank distillation, flat tank distillation or electric furnace; wet zinc smelting has been rapidly developed in the past 20 years, and currently 70% to 80% of total zinc production is produced by wet method. The crude zinc obtained by the pyrometallurgical zinc is refined or directly applied by distillation; and the electrolytic zinc obtained by the wet zinc smelting is of high quality and does not require refining.

For the difficult-sorted lead-zinc sulfide concentrate, it is generally treated by a closed blast furnace smelting method that simultaneously produces lead and zinc.

For the extremely difficult to sort lead oxide-zinc mixed ore, after long-term research, China's unique treatment method has been formed, that is, the lead or zinc mixed ore or its enriched product is sintered in a blast furnace after sintering or pelletizing, so as to obtain coarse Lead and lead-zinc-containing molten slag, the slag is further fumed in a fuming furnace to obtain a zinc oxide product, and zinc is obtained by wet zinc smelting. In addition, it is also possible to obtain a zinc oxide product by direct smoulding in a rotary kiln.

Second, the impact of concentrate impurities on lead and zinc smelting

(1) Impurities in lead concentrate:

Copper : The presence of copper-containing sulfides in the concentrate. Sintering at the firing temperature, the reaction of copper oxide, metallic copper is reduced to the time, into the crude lead, high lead containing copper as thick (> 2%), you need ice making copper smelting copper recovery, otherwise, melting When it is difficult to separate lead and slag, it is easy to block the siphon channel, which causes handling difficulties, affects workers' health and lead volatilization loss. When the amount of copper in the lead product is high, the lead is hardened. Therefore, the copper content in the lead concentrate is required to be <3%, and the mixed concentrate contains <1% copper.

Zinc: It is present in the zinc concentrate in the lead concentrate and becomes ZnO upon firing. In the process of smelting, there is no chemical change, most of which enters the slag, increases the viscosity of the slag, and reduces the difference in specific gravity between the lead liquid and the slag, which makes the separation of the two difficult and affects the recovery rate of lead. Part of the ZnO may condense on the furnace wall to form a furnace junction, making operation difficult. When the zinc content in the raw material is high, it will cause high iron slag and increase the loss of lead in the slag. Zinc tends to harden lead metal and cannot be pressed into flakes, and promotes the corrosiveness of sulfuric acid to lead. Therefore, lead concentrate is required to contain no more than 10% zinc.

Arsenic : It exists in the state of toxic sand (FeAsS) and realgar (As ₂ S ₃ ) in the concentrate. When it is smelted, it is partially reduced to As ₂ O ₃ and volatilized into the flue gas to form extremely harmful atmospheric pollution. Part of As enters into crude lead and slag; when As contains high As, it is necessary to remove As by alkaline refining method, and Na ₃ AsO ₄ contained in the produced scum is highly soluble in water and pollutes water source, causing poisoning of humans and animals. . Arsenic is easy to form an alloy with lead, which hardens lead. Therefore, arsenic in lead concentrate is required to be no more than 0.6%.

Magnesium oxide (MgO): a melting point of 2800 deg.] C, the melting point of the slag increases, and easy to reduce the solubility of the iron oxide in the slag, the slag becomes viscous, typically containing up to 3.5% MgO, frequently the fault, it is desirable lead concentrate containing MgO is not more than 2%.

Aluminum oxide (Al ₂ O _3): a melting point of 2050 deg.] C, the melting point of the slag increases, viscosity increases, especially in combination with ZnO as gahnite _{(ZnO • Al 2 O 3)} , in a blast furnace-based material does not melt, so that The melting point and viscosity of the slag are significantly increased, so the Al ₂ O _{3 in the} concentrate is required to be no more than 4%.

(2) Impurities of zinc concentrate:

Copper: In the concentrate, copper is often present in the sulfide state. When calcined, different forms of cuprous oxide are formed, and the residual copper sulfide is easy to form matte, which lowers the melting point of the charge. When wet zinc smelting, the Cu ⁺ + corrosion pipeline in the solution, the valve, when distilled in the vertical tank, often has a small amount of crude zinc, which affects the quality of commercial zinc. Therefore, the zinc concentrate is required to contain no more than 2% of Cu.

Lead: When zinc sulfide contains high levels of lead sulfide, it forms fusible lead sulfur. Lead sulfur first promotes agglomeration and even melts the calcined material, preventing the removal of sulfur. Lead oxide tends to form a low melting point eutectic with many metal oxides, starting to melt at 800 ° C, causing the charge to agglomerate in the boiling furnace and the flue. In the wet method lead smelting, when the blast is leached, it is converted into lead sulfate and consumes sulfuric acid. In the pyrometallurgical lead, the lead oxide is reduced in the distillation tank, partially vaporized, and condensed into impurities in the zinc ingot, which affects the quality of the commercial zinc. The lead sulfate in the roasting ore is reduced to lead sulfide in the distillation tank. , and other metal sulfides can form matte, causing corrosion of the tank wall. Therefore, zinc concentrate is required to contain no more than 3% lead.

Iron: Iron forms zinc ferrite when calcined in the presence of iron sphalerite in the zinc concentrate. In the wet zinc smelting process, zinc ferrite is not dissolved by dilute acid, which affects the leaching rate of zinc and increases the treatment cost of leaching slag. The free FeS in the concentrate is converted to Fe ₂ O ₃ when calcined, and FeSO ₄ enters the solution when leaching with sulfuric acid. When oxidized and neutralized, flocculent Fe(OH) _{3 is formed} , which affects the clarification speed of the thickener. In the vertical distillation of the fire method, the Fe ₂ O ₃ in the calcined ore is reduced to FeO and metallic iron, wherein the metal iron forms iron in the vertical tank, which affects the temperature rise of the vertical tank, and the zinc evaporation is insufficient, resulting in the slag. High in zinc content; when SiO ₂ is present in the ore, it is easy to form silicate with the FeO to erode the tank wall; when the crude zinc enters the distillation tower, the iron content of the crude zinc directly affects the life of the tower. Therefore, it is desirable that the zinc concentrate contains no more than 16% iron and the wet zinc smelting is not more than 10%.

Arsenic: Arsenic contains arsenic. When boiling and roasting, arsenic enters the flue gas, causing V ₂ O _{5 to be} poisoned by coal when sulfuric acid is produced. Most of the arsenic in the calcined ore is removed during leaching, but the solution containing As is high, the consumption of FeSO _{4 is} large (the amount of iron is 20 times the amount of arsenic), the iron is more slag, and more zinc is taken away. As can be discharged on the cathode to cause a burn-in phenomenon (cathode back-melting). Therefore, the As in the concentrate mixture is required to be no more than 0. 5%.

Silica: Concentrates often contain free SiO ₂ and various bound state silicates, forming zinc silicate with zinc oxide at high temperatures. In the wet leaching, the silicic acid enters the solution in a colloidal state to concentrate the product, and the filtration process is extremely difficult. Under the high temperature conditions of the distillation process, SiO ₂ forms a silicate with CaO, FeO, etc., and corrodes the tank wall to hinder distillation. It is required that the SiO _{2 in the} concentrate is not more than 7%.

Fluorine: Fluorine in boiling roasting flue gas easily corrodes the acid system tile and damages the equipment. When the fluorine content in the electrolyte is high, the cathode zinc is not easily peeled off. It is required that F in zinc concentrate is not more than 0.2%.

3. Comprehensive recovery of associated components in lead and zinc smelting

(1) Comprehensive recovery during lead smelting:

Sulfur: Sulfuric acid is recovered from the flue gas of the sintering machine.

Copper: In the case of blast furnace smelting, it is recovered as matte or in the form of copper scum during pyrometallurgical refining.

é“Š : It is recovered in the sintered soot.

Gold, silver, platinum group metals, selenium, tellurium and bismuth: electrolytic refining anode mud recovery, recycling or pyrometallurgical refining dross.

Zinc: recovered by smouldering in blast furnace slag.

Cadmium : It is recovered in soot.

(2) Comprehensive recovery during zinc smelting:

Sulfur: recovered in boiling roasting flue gas.

Lead: recovered in zinc oxide leach residue.

Gold, silver: recovered as concentrate in the leaching residue by flotation.

Cadmium: recovered in copper cadmium slag.

Copper: recovered in copper cadmium slag.

Indium , gallium , and antimony : recovered in indium bismuth slag.

Cobalt : recovered as cobalt slag in the case of clean liquid.

é“Š: Recovered in the dust removal process of the chlorofluorocarbon process (multi-hearth furnace or rotary kiln).

Fourth, the calculation method of industrial grade indicators in mining areas

According to the geological data available in the census evaluation stage and the technical and economic indicators of the general production of domestic lead and zinc mines, the calculation of the industrial grade of the mining area (referring to the average grade of the mining area) can be carried out by a simple and easy “price method”.

The "price method" formula is as follows:

1. Complete cost of one ton of ore: the sum of mining, ore dressing , raw ore transportation cost, enterprise management fee and concentrate sales fee for each ton of raw ore:

Mining cost: mining cost, different development methods (flat, shaft), different mining methods, displacement, etc., all affect mining costs. At present, the mining cost of underground mining in China is about 12~23 yuan/ton, and that of large and medium-sized mines is 10~28 yuan/ton.

Mineral processing cost: Lead-zinc ore is generally flotation, and its ore dressing cost is affected by factors such as ore content, mineral size, chemical consumption, and tailings transport distance. At present, the flotation cost of flotation is generally 10 to 16 yuan / ton.

Raw ore transportation cost: refers to the transportation cost of the ore from the pit to the plant, affected by the distance of transportation and transportation mode (motor car, cableway, etc.). At present, China's pit mining mountains are generally 1 to 1.5 yuan / ton.

Enterprise management fee: Enterprise management fee is affected by the size and management level of the enterprise. At present, China's large and medium-sized enterprises are 2 to 4 yuan/ton, and small enterprises are 3 to 5 yuan/ton.

Concentrate sales fee: All the expenses (transportation fee, handling fee, management fee, etc.) of the lead-zinc concentrate from the mine selection plant to the delivery location of the smelter are concentrate sales fees. The transportation fee can be calculated according to the distance between road, railway and water transportation and the freight rate stipulated by the relevant department. However, when participating in the calculation of the above formula, the concentrate sales fee shall be converted into the original mine sales fee.

2. Mining depletion rate: Due to different geological conditions, different mining methods and management levels, there are differences in mining depletion rates. At present, the depletion rate of pit mining in China is generally 10% to 25%.

3. Concentration recovery of ore dressing: According to the test results of ore selectivity in specific mining areas, the indicators are selected.

4. Concentrate contains metal price per ton: the current price stipulated by the state, and the unit of price is the metal per ton contained in the concentrate.

Because in the formula, the concentrate sales fee needs to be converted into the original mine sales fee, and the concentrate quantity is difficult to determine under the condition that the grade has not been determined, so the distribution is difficult. To avoid this problem, the following formula can be used instead. In the following formula, the full cost of one ton of ore does not include the cost of the conversion of the concentrate sales fee.

The concentrate price in the formula needs to be converted. For example, when the zinc concentrate contains 55% Zn, the price per ton of metal content is 1010 yuan, and the price per ton of concentrate is 1010 yuan × 55% = 555.5 yuan.

The concentrate sales fee in the formula is the sales fee per ton of concentrate, which is not converted into the original ore cost.

In the geological evaluation of each specific mining area, the parameters of the specific mining area can be substituted into the above formula to determine the industrial grade of the mining area, so as to evaluate the economic significance of the mining area.

According to the calculation of the general technical and economic indicators of lead-zinc production in China, and the actual production data of some mines, the general requirements of industrial grades in the mining area are 4% to 5% of sulfide ore Pb+Zn, 6% to 8% of mixed ore Pb+Zn, and 8% of oxidized ore Pb+Zn. ～10%, this data can also be used for economic evaluation of deposits and to consider whether the mining area is transferred to detailed exploration. This data can be reduced as appropriate for mines that are easy to pick and choose, have convenient transportation, and mines that produce mines. In the future, considering the continuous improvement of mine management and mining technology, the reference data of industrial grades in the above-mentioned mining areas will inevitably be gradually reduced.

Calculating the industrial grade of the mining area, there are other methods besides the "price method", but many of them are more complicated than the above methods. Considering the limited information available in the census stage, they are not listed one by one, and can be understood by the industrial design department if necessary. .

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