Modified equilibrium-solubility domains and a kinetic model of iron oxide and hydroxide colloids for electroflocculation

Water for reuse, or wastewater containing a high concentration of iron particles, often requires particle destabilization and removal. This paper studies the chemical flocculation (CF) of iron colloids as well as modified equilibrium-solubility domains and a kinetic mathematical model for electroflocculation (EF). ζ-potential measurements and the stability constant of the iron ligands call for a comparison of equilibrium the constant and help to build a modification of the equilibrium-solubility domains. The modification for EF and CF show similar results as those yielded by Stumm and O'Melia [1], except that the concentration of Fe(OH)₃(s) is smaller. The values, appearing as cross-hatched areas, indicate the range of coagulant dosages that are normally used in water treatment. From these results one might be tempted to conclude that the species involved in coagulation are the insoluble iron hydroxide precipitates. The overall kinetic model of flocculation in turbulent mixing for EF was modified by Argaman and Kaufman [2] and applied by Bratby [3] to plug flow behavior. Modifying these equations for EF is effected by determining the values K_B′ (breakup constant) and K_F′ (flocculation constant). It should be noted that the empirical relationship between breakup constant K_B and flocculation constant K_F in CF and K_B′ and K_F′ in EF may explain the difference between these two processes. The results from the experiments exhibit a different behavior between CF and EF. The empirical relationship between these parameters in CF and EF improve the relationship attained by the mathematical model.