ELSEVIER Hydrometallurgy43 (1996) 155-167 hydrometallurcjy Flotation of molybdate oxyanions from dilute solutions Part II. Selective separation from phosphates, arsenates and silicates Y.-C. Zhao, A.I. Zouboulis *, K.A. Marls Chemical Technology Division, Department of Chemistry, Aristotle University, GR-540 06 Thessaloniki, Greece Received 26 November 1995; accepted 27 January 1996 Abstract Adsorbing colloid flotation was found to be an efficient method for selective separation of phosphates or silicates from aqueous solutions of molybdate oxyanions (binary mixtures); tertiary and quaternary mixtures of molybdates and arsenate, phosphate and silicate anions have been also separated effectively. The main parameters affecting this process, namely the concentrations of Fe(III) (used as co-precipitant), dodecylamine (used as surfactant or collector), molybdates, phosphates, arsenates and silicates, the pH of the solutions studied, as well as the addition of foreign ions (CI- and SO2-) were investigated in detail. It was found that over 95% of the impurities (usually 15 mg/1 each) can be selectively removed from aqueous solutions containing molybdates (at concentrations exceeding 200 mg Mo/l), when the solution pH was around 9 (+ 0.2), while the simultaneous co-removal (i.e. loss) of molybdates was around 20%, almost regardless of the initial concentrations of the other co-existing components. Keywords: flotation (adsorbing colloid); separation; oxyanions; molybdate; arsenate; phosphate; silicate 1. Introduction In our previous work, the quantitative removal of toxic molybdate and arsenate ions from dilute aqueous solutions, considered as wastewaters, by flotation [1] (the environ- mental point of view), as well as the selective separation of molybdate from arsenate ions, existing in binary mixtures [2] (the hydrometallurgical point of view) were * Corresponding author. 0304-386X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PH S0304-386X(96)00011-4