STUDIES ON THE COAGULATION AND FLOCCULATION OF COAL WASHERY EFFLUENT: A KINETIC APPROACH

Abstract

The effect of coagulant type, coagulant dosage and pH variation on the coagulation of coal washery effluent has been investigated at room temperature using various coagulants. Turbidity measurement was employed using the nephelometric standard method. In addition, the coagulation reaction rate constant, K, the order of reaction, a and the distribution of particles were also determined.

The results show that for coagulant mixture containing FeCl₃, and lime, the maximum turbidity removal occurred at pH of 4 and 2 for the FeCl₃/lime ratio of 30:400 and 500:1000 respectively. The least and highest values for order of reaction (a) recorded for the dosage variations are 2.0 and 3.0 respectively. With the exception of a value computed for 50 mgl^-1 FeCl₃+1000 mgl^-1 lime, there is no regular pattern in the variation of a in response to the increment of pH from 2 to 10. The over all results show that with the exception of few blends, the computed order of reaction, α, and rate constants, K, agree with previous works reported in the literature.

It is concluded that jar test and nephelometric method still provide the convenient and routine means flocculation studies. The results obtained confirmed that the theory of fast coagulation holds for the coagulation of coal washery effluent using the coagulants investigated and at the conditions of the experiment.