Which one of the electrolyte is reqiured in minimum quuantity to coagulate a negatively charged suspenstion of clay in water ?

According to Hardy-schulze rule, Greater the valency of flocculating ion(of the electrolyte) greater is its power to coagulate the oppositely charged colloidal sol.  Clay is a negative sol, it is coagulated by positive ion;Coagulating power ∝1Coagulation valueThe minimum millimoles of the electrolyte required to coagulate one litre of colloidin two hours is called floculating (or) coagulation value.So Aluminium chloride is required in minimum quantity;