Charge-neutralizing inorganic coagulants — aluminum sulfate, ferric chloride, and polyferric sulfate — for clarifying source water and wastewater and for chemical phosphorus removal.
Inorganic coagulants are metal-salt chemicals — aluminum and iron(III) salts — that neutralize the negative surface charge on suspended colloids, so fine particles, color, and phosphate collapse out of water and can be removed by settling or filtration. In water treatment they are the first chemical step in clarifying raw, process, and waste streams. Match the coagulant to source-water pH and to the contaminant you are targeting.
The page carries three charged metal salts, with a real trade-off between cost and pH tolerance. Aluminum sulfate (alum) is the low-cost workhorse, but it works in a narrow band near pH 5.5 to 7.5 and consumes alkalinity. Ferric chloride and polyferric sulfate stay effective across a wider pH range, settle a denser floc, and strip phosphate well — at higher cost and with more corrosive handling. Specify alum for routine clarification at controlled pH; specify the iron salts for cold water, color, phosphorus removal, or variable pH.
Coagulants act in seconds and need rapid mixing; flocculation and settling follow. Jar-test the dose — typical alum doses run tens of milligrams per liter but shift with turbidity and temperature — because overdosing depresses pH and re-stabilizes the particles you meant to drop. Where a permit drives low total phosphorus, the iron salts at a molar Fe:P ratio set by the target residual are the usual route.
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