Heavy metal removal process used in zinc borate preparation process

Abstract

The invention discloses a heavy metal removal process used in a zinc borate preparation process. The heavy metal removal process is achieved through three-stage control of zinc sulfate purification, zinc borate synthesis and purification and mother liquid purification, that is, the content of heavy metals introduced into a raw material, namely zinc sulfate, is controlled, a distribution ratio of the heavy metals to zinc borate is controlled, and the content of heavy metals in a mother liquid which is used indiscriminately in a circulation manner. By using the three-stage control method of source removal, process distribution and mother liquid accumulation, heavy metals in the whole zinc borate preparation process are removed, preparation of high-quality zinc borate of a low heavy metal content is achieved, and the competitiveness of the domestic zinc borate in international markets is greatly improved.

Description

technical field [0001] The invention relates to a heavy metal removal method, in particular to a heavy metal removal process in the preparation process of zinc borate. The invention belongs to the field of halogen-free flame retardants. Background technique [0002] Zinc borate (Zinc borate) is an environmentally friendly non-halogen flame retardant, depending on the composition (XZnO 3 ·YB 2 O3·ZH 2 O), there are more than a dozen varieties of zinc borate flame retardants. The most commonly used variety is 2335 type zinc borate, which has the characteristics of non-toxicity, low water solubility, high thermal stability and good dispersibility. [0003] As an efficient flame retardant, 2335 type zinc borate is widely used in plastics, rubber processing, transportation, aerospace, fiber fabrics, ceramic glazes, coatings and other fields. As a multifunctional synergistic additive of antimony oxide or other halogen flame retardants, it can effectively improve the flame ret...

AI Technical Summary

Problems solved by technology

[0005] In order to solve the problem that the heavy metal accumulation in the process from commercially available zinc sulfate to zinc borate products in the zinc borate production process causes the heavy metals in the final product to exceed the standard, the present invention divides the zinc borate production process into three sections to carry out the heavy metal removal and purification technology respectively, (1) Zinc sulfate purification: use active zinc powder to replace and purify the commercially available zinc sulfate, and initially remove most of the heavy metals (including Pb, Cd, Mn and other inactive heavy metals); (2) Zinc borate synthesis and purification : By adding sulfuric acid to the boric acid-zinc hydroxide synthetic zinc borate reaction system, the acidity of the system is enhanced, the distribution ratio of heavy metals in the mother liquor / zinc borate product is changed, and the accumulation of heavy metals in the product is reduced; (3) mother liquor purification: due to boric acid The zinc mother liquor needs to be recycled in the process, and the heavy metal impurities will accumulate batch by batch. In order to solve the problem of the mother liquor, it is necessary to further replace and purify the boric acid mother liquor with active zinc powder to reduce the heavy metals in the mother liquor to an acceptable range.

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