Multivalent metal ions inorganic coagulants

The potential for ion adsorption allows for two further coagulation mechanisms. The first may be described as adsorption destabilisation and ultimately has a similar effect to that described for indifferent electrolytes. Metal ions effectively act to neutralise particle charge, reduce the extent of double layer repulsive interactions and hence decrease the potential energy barrier to coagulation. The second, and perhaps more important, mechanism may be 

While metal ion coagulants such as aluminium sulphate are widely used as reagents in potable water treatment (for instance), their tendency to form 

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Although some inorganic salts can act as indifferent (non-adsorbing) electrolytes, the more important types of coagulant from a process engineering viewpoint are the salts of multivalent metal ions such as Ca, Fe +, Fe and Al +. These ions hydrolyse or specifically adsorb to particle surfaces to induce coagulation. 

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