Coagulant

Magnesium sulfate is the coagulant used in making tofu. It causes the liquid soy milk to separate into solid tofu and water.

Aluminum also is an incrustant present in most waters in quantities so small that it is not necessary to consider it; but when too much aluminum sulphate, a substance frequently used as a coagulant in filtering water, is added in the process of filtering, the excess passes through the filter and may cause trouble in the boiler, where it hydrolyzes, forming free sulphuric acid.

Primary stage – removal of insoluble particulate material by screening, the addition of coagulants, followed by settlementation.