Premix discoloration is a very common phenomenon, it is mostly caused by the impurity and high moisture content in feed additive, and also because of high content of carbonate in raw material. Take feed grade zinc sulfate and ferrous sulfate as examples
Feed grade ferrous sulfate, made from heels of the Titanium Dioxide factory, titanyl sulfate residual and Fe3+ is the direct reason for discoloring, if ferrous sulfate is dried not purified before drying.
For feed grade zinc sulfate, factories add superfluous peroxide to remove Fe to make products more beautiful, and the residual peroxide reacts with titanyl sulfate, making some coloring materials.
