Smelting method:
There are two main methods of modern nickel production: fire method and wet method. Depending on the two main types of nickel-containing minerals in the world (nickel-containing sulfide ores and oxide ores), smelting and processing methods vary.
Nickel-containing sulfide ores are currently mainly processed by fire treatment. Metallic nickel is obtained by smelting copper, nickel and sulfur in a reverberatory furnace (electric furnace or blast furnace), blowing nickel concentrate, and electrolyzing nickel concentrate. Oxidized ore is mainly nickel-containing laterite ore, which is of low grade and suitable for wet treatment; the main methods are ammonia leaching and sulfuric acid. The fire treatment of oxide ore is the ferronickel method.
Processing operations:
Pyrometallurgy of nickel sulfide concentrate
The pyrometallurgy process of nickel sulfide concentrate is shown in Figure 29-2. Its main process features are as follows:
(1) Smelting. After drying and desulfurization, the nickel concentrate is sent to an electric furnace (or blast furnace) for smelting. The purpose is to convert the oxides of copper and nickel into sulfides to produce low nickel matte (copper-nickel matte) and at the same time gangue slagging. In the obtained low matte nickel, the total content of nickel and copper is 8-25 (generally 13-17), and the sulfur content is 25.
(2) Blowing of low nickel matte. The purpose of blowing is to remove iron and part of the sulfur to obtain high matte nickel (nickel high sulfur) containing 70-75% copper and nickel, not metallic nickel. The converter melting temperature is higher than 1230°C. Due to the low grade of low-ice nickel, the blowing time is generally longer.
(3) Grinding and floating. After fine grinding and crushing of high matte nickel, it is separated by flotation and magnetic separation to obtain nickel concentrate containing 67-68 nickel. At the same time, copper concentrate and copper-nickel alloy are selected to recover copper and platinum group metals respectively. The nickel concentrate is melted in a reverberatory furnace to obtain nickel sulfide, which is then sent for electrolytic refining or reduced and smelted through an electric furnace (or reverberatory furnace) to obtain crude nickel, which is then electrolytically refined.
(4) Electrolytic refining. In addition to copper and diamond, crude nickel also contains gold, silver and platinum group elements, which need to be recycled by electrolytic refining. Different from copper electrolysis, a diaphragm electrolytic cell is used here. Crude nickel is used as the anode, the cathode is a nickel starter piece, and the electrolyte is a mixed solution of sulfate solution and sulfate and chloride salt. After energization, nickel precipitates from the cathode, and platinum group elements enter the anode mud and are recycled separately. The purity of the product's electro-nickel is 99.85-99.99.
Use pyrometallurgy to treat nickel oxide to produce ferronickel and metallic nickel
Silicate oxide ore can be smelted by pyrometallurgy, and nickel can be obtained through reduction, melting and refining. During reduction, strive to completely convert nickel oxide into metallic nickel. When melted the ferronickel will separate from the lighter slag. The nickel content of ferronickel depends on the selectivity of the partial reduction process. Coke is used as the reducing agent, and ferrosilicon can also be used as the reducing agent. In order to remove the impurities carbon, sulfur, phosphorus and chromium in crude nickel iron, refining must be carried out.
Refining ferronickel by direct partial reduction with carbon in an electric furnace
The ore is reduced to ferronickel by carbothermal method in a submerged arc furnace and subsequently refined.