The coagulant action of lime neutralizes the negative charge on colloid particles contained in water. It also causes the flocculation of suspended impurities which makes decanting easier. Lime acts as the flocculating agent to which metallic salts and/or polymers can also be added. The use of lime to increase pH levels can precipitate most heavy metals in the form of hydroxides. When waste waters contains phosphates and sulfates, lime makes it easier to precipitate them as well as the heavy metals, in the form of insoluble salts - Ca3(PO4)2, CaSO4 - that are easier to collect.