Colloids and Surfaces, 53 (1991) 275-295 Elsevier Science Publishers B.V., Amsterdam 275 zyxwvutsrq Photooxidative dissolution of CdS (s) Part I. Important factors and mechanistic aspects Y.H. Hsieh’ and C.P. Huang” ~nuir~nrne~ta~ Engineering Program, Wnivers~~~ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO of ~e~~~~re, Newark, DE 19716 (U.S.A.) (Received 4 November 1988; accepted 20 August 1989) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Abstract Important factors such as pH, ph(~toin~nsity, dissolved oxygen, solid concentration and tem- perature on the oxidative dissolution of CdS(s1 were studied. Results indicated that photoirra- diation plays the most important role in CdS (s) dissolution. The mode of dissolution is signifi- cantly affected by pH and dissolved oxygen. A qualitative mechanism was proposed to describe the dissoIution reaction under various ambient conditions, namely, light/darkness and aerobic/ anaerobic. INTRODUCTION The ~ssolution of minerals in aqueous solutions is an important process controlling the transport and transformation of chemical species in natural waters [l-6]. Among the various minerals of environmental significance, the sulfide minerals, due to their uniquely low solubility and sensitivity to redox potential, have been the most notorious environmental solids. It has been re- ported that sulfide formation controls the concentrations of trace metal ions in pore waters [ 7 3. We have selected cadmium sulfide as the major solid for investigation. Cadmium sulfide is characterized by an extremely low solubility in aqueous solution [8]. In the presence of oxygen, CdS (s) is unstable and can be readily dissolved 19 1. The dissolution of CdS (s ) in aqueous solution has significant environmental consequences. Upon irradiation with light, cad- mium sulfide can undergo photoinduced oxidative dissolution reactions by which cadmium ions are released into the solution and sulfide ions are oxidized to sulfate [lo]. In recent years, the use of CdS(s) dispersions in several pho- tosynthetic and photocatalytic reactions has been extensively investigated [ ll- 151. Very little is known about the mode and the rates of cadmium sulfide ‘Current address: Department of Environmental Engineering, National Chung Hsing University, Taichung, Taiwan. ‘To whom correspondence should be addressed. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF 0166-6622/91/$03.50 0 1991- Elsevier Science Publishers B.V.