EFFECTS OF PH, IONIC-STRENGTH AND A FULVIC-ACID ON SIZE DISTRIBUTION AND SURFACE-CHARGE OF COLLOIDAL QUARTZ AND HEMATITE

Size distribution of colloidal quartz and hematite (initial diameter 1 40-190 nm and 70-360 nm, respectively) were determined by Photon Corre lation Spectroscopy (PCS) in well-defined laboratory systems. Effects on the mean diameter and the size distribution were measured at variou s values of pH (2-12) and ionic strength (0.001-0.7 mol/1) in an inert medium (NaClO4). The effect of an aquatic fulvic acid on the stabilit y of the colloids was included in the study. In the absence of fulvic acid the colloids flocculate at a pH close to pH(zpc) of the respectiv e mineral. This increase in mean diameter is due to electrostatic inte ractions. Hematite colloids are also destabilised at a pH much below p H(zpc). The quartz colloids are stabilised in the presence of fulvic a cid. The hematite/fulvic acid systems are stable at high pH, but flocc ulate at low pH. Increasing ionic strength induces agglomeration of th e quartz colloids at 0.1 mol/l, independently of the presence of fulvi c acid (2 mg/1). Hematite is destabilised at 0.02 mg/l in the absence of fulvic acid, while in the presence of fulvic acid the colloids aggr egate at ionic strength >0.07 mol/l.