Fire smelting - traditional process of electrolysis

The traditional treatment process for lead anode mud is fire smelting - electrolysis. Before expensive pyrometallurgical smelting of lead typically to remove selenium, tellurium (including copper also include high copper removal), by reduction smelting pyrometallurgical Degui copper, lead and then by oxidation refining expensive, silver gold alloy sheet feeding output electrolytic silver . After the silver anode mud is properly treated, the anode is cast for gold electrolysis.

1. Lead anode mud removes selenium and tellurium

Some factories are pre-baked to remove selenium and tellurium before pyrometallurgical smelting, but there are also some factories that recycle slag in precious lead oxidative refining. The latter is similar to the operation of oxidizing and melting slag in the silver furnace by the lead lead obtained by smelting lead anode mud.

(1) Baking in addition to selenium and tellurium

In the process of roasting and removing selenium, the lead anode mud and concentrated sulfuric acid are uniformly mixed. The sulphation roasting is carried out in a rotary kiln, the temperature starts at 300 ° C, and finally the temperature is gradually raised to 500-550 ° C to make the selenium SeO ₂ play, and the absorption tower generates H. ₂ SeO ₃ , H ₂ Se ₃ reacts with SO ₂ in the flue gas to form elemental selenium (crude selenium), and then refined to obtain refined selenium. Calcine crushed by leaching with dilute H ₂ SO _4, 70% of pounds can enter dissolved, then zinc powder obtained tellurium mud replacement. The mash is then calcined by sulphation, the ruthenium is oxidized, and the ruthenium is leached with NaOH. The leaching solution is filtered to obtain a ruthenium electrolyte, and the pure ruthenium is obtained by electrowinning. The total recovery of ruthenium is about 50%.

(2) Muffle furnace roasting in addition to selenium and tellurium

The lead anode slime and concentrated sulfuric acid are mixed and placed in a muffle furnace for calcination, and pre-calcined at a temperature of 150 to 230 °C. Then, the calcined material is introduced into the muffle furnace and calcined and desulfurized at 420-480 ° C. The selenium is volatilized in the form of SeO ₂ , and the volatilization rate is 87-93%. The calcined sand is crushed, then leached with hot water, and then replaced with zinc. The mud is obtained, and then the mash is recovered by alkali leaching-electrolysis.

Second, lead anode mud fire method melting

The lead anode mud can be smelted separately or in combination with a copper anode mud which is decoppered or selenium. The mixing process of copper and lead anode mud is shown in Figure 1. The lead anode mud and the copper anode selenium decoppered copper are mixed in proportion and placed in a converter for reduction smelting. The material to be dispensed into an appropriate proportion of flux, usually crushed coal powder or coke dust, limestone, soda or fluorite and scrap iron. Iron filings are added to remove lead and antimony from the compound and to increase slag fluidity. When the anode slime contains high iron, it does not have to be blended. The reduction smelting generally uses a converter or a reverberatory furnace, and the fuel is mostly heavy oil or diesel oil. It is smelted in a reverberatory furnace, and the furnace mouth must be tied before feeding. The furnace mouth is first cleaned of precious lead or debris on the mouth of the reverberatory furnace, then a coke powder, two parts of clay are mixed, a small amount of water is added and the mud is placed on the mouth of the furnace, and a layer of iron pipe is used. One layer of solidity. A solid furnace mouth is a very important operation. For example, if the furnace mouth is not cleaned, when the furnace temperature rises, the melting of the low-melting precious lead will cause a serious "running furnace" accident. After the charge gradually warms up to the melting period, the molten pool is agitated to accelerate the melting. After all the furnace materials have been melted for about 8 hours, the molten pool is thoroughly stirred once to prevent the charge from sticking to the bottom. After clarification for more than 1h, the upper layer of silicate and arsenate dilute is released, and the slag is extracted. In order to reduce the metal loss in the slag, it is also possible to heat the slag and heat the mixture for 1 hour to precipitate the precious lead contained in the slag, and then slag the slag. In order to improve the grade of precious lead, some factories keep the furnace temperature at 900 °C after removing the slag, and use the air duct to oxidize the metal liquid surface. When the white smoke to the liquid level of the molten pool is small, the air is blown and precipitated. Baked out. The total amount of precious lead produced contains gold and silver in the range of 30% to 40%.

Figure 1 Lead, copper, anode mud mixing process

Third, the oxidation of precious lead

The oxidative refining of precious lead generally uses a converter. When you lead eluted at a low temperature of 700 ~ 900 ℃, copper, iron and its compounds (including antimony copper arsenide, copper, etc.) due to high melting point, and floating on the liquid surface. At the same time, various high-melting-point impurities which are not alloyed with noble lead are also subjected to segregation separation, and together with lead iron and a compound thereof constitute a dry residue. After the dry residue is removed, it is oxidized by blowing, and nitrate is added to strengthen the oxidation in the late stage of blowing oxidation. In the smelting process, when it is necessary to recover lanthanum and cerium for raw materials containing cerium and lanthanum, slag and slag are required to recover lanthanum and cerium, respectively.

The gold and silver alloy anodes produced by the smelting in the silver furnace are sent to the electrolytic refining silver, and the gold is recovered from the silver anode mud.