The content of Pb, As, Cd must be strictly controlled when zinc sulfate was produced, because they are all harmful trace element to animals. In international standard for feed grade zinc sulfate, the content should be no more than 10 mg/kg; But because of some reasons such as having not tested the raw material, and lacking of advanced testing machines, lots of zinc sulfate produced by SMES are not qualified in heavy metals content. It will be harmful to animals, for these heavy metals will not be digested and will stay in the animals’ bodies, which will be harmful to human’s health finally.
Firstly, it can be controlled on the source of zinc sulfate, because poor quality zinc oxide and sub-zinc oxide are the major source of heavy metals. So it must be pre-testing when purchasing raw materials and make records for qualified materials to assure products’ quality and quality track.
Secondly, manufacturers can improve the technology and remove impurity thoroughly, and controlled the heavy metals content at the lowest.
Thirdly, adopting the most advanced inspecting machine: polarographic analyzer and spectrophotometer to test heavy metals accurately.
