Several common production processes of zinc oxide: direct method (American method), indirect method (French method), chemical precipitation method (wet method) and a method of processing feed zinc oxide by the by-product of production of insurance powder.
The metals in the raw materials containing zinc mainly exist as oxides, such as zinc oxide, copper oxide and cadmium oxide. When zinc oxide reacts with coke, it is reduced to metallic zinc by steam and then oxidized to zinc oxide by oxygen in the air. Most heavy metals are removed. Direct method zinc oxide is white powder, coarse grain, high content of products, generally used in rubber, ceramics industry. In feed industry, southeast Asia is useful this kind of zinc oxide.
A metal zinc ingot or zinc residue obtained from the smelting of ore is converted into zinc steam by heating and oxidized to zinc oxide by oxygen in the air.
The heavy metal content of the product depends entirely on the quality of the zinc ingots or zinc slag used. Can be used in rubber, ceramics, electronics and other industries. When choosing high quality zinc ingots, the heavy metal content of zinc oxide is low. In fact, many indirect zinc oxide products on the market today use zinc slag as raw material, rather than pure zinc ingots. Therefore, the heavy metal content in products is often relatively high.
The production process of indirect zinc oxide is simple and its price is mainly determined by the price of its raw material. This kind of zinc oxide particle size is more micron grade, domestic used more, now very few.
This method can be roughly divided into two categories, namely, acid method and ammonia method. They react with the raw material using either an acid or a base, which is then purified and given basic zinc carbonate, which is calcined to produce the final product light zinc oxide, or active zinc oxide.
(a) the acid process usually involves the reaction of zinc containing raw materials with sulfuric acid to obtain a very pure zinc sulfate solution containing heavy metal ions. Then the pure zinc sulfate solution is obtained through oxidizing, reducing and removing impurities, and multiple precipitation, removing a large amount of plasma of iron, manganese, copper, lead, cadmium and arsenic. The solution is neutralized with a soda to obtain solid zinc carbonate. The active zinc oxide can be obtained by washing, drying and burning.
(b) the ammonia method usually USES ammonia water and ammonium carbonate to react with the raw materials containing zinc to obtain the zinc ammonia complex, and then remove impurity to obtain the qualified zinc ammonia complex solution, which is then steamed to convert the zinc ammonia complex into basic zinc carbonate. Finally, the active zinc oxide can be obtained by drying and calcining.
If the above two methods are controlled reasonably, the nanometer zinc oxide with particle size between 1 and 100 nanometer can be obtained.
However, there are differences between the two methods: the acid method has an absolute advantage in product quality, because the acid process can remove the heavy metal from raw materials cleanly, and the particle size of zinc oxide is easier to control; The ammonia method has obvious advantages in cost, because it can recycle the intermediate, but in quality control, it needs to control the content of arsenic.
This method has certain difficulty in the control of arsenic, in addition, its particle size is easy to become coarse. The color of zno is yellow because of the properties of nanoparticles.
The yellow of zinc oxide by ammonia method is not obvious, almost white.
The above situation is not absolute, because the process details of each manufacturer also affect the product characteristics.
For example, not all products of acid method can reach nanometer level, depending on the completion level of this process.
The production process of nano-zinc oxide is complex, and its price is affected by many factors such as raw materials, auxiliary materials, equipment and process cost.
There is a lot of use of zinc oxide on the market, the bulk density is very large, colloquially speaking, it is very heavy, yellow color.
It is obtained by the high temperature calcining of zinc hydroxide, a by-product of the production of insurance powder.
Like the direct method and indirect method, it can also be attributed to zinc oxide of fire method. Its characteristics are coarse particles and small specific surface area.