不同pH、电解质浓度条件下草酸对针铁矿吸附Cd(II)的影响及机制

用吸附平衡法研究了不同草酸浓度、体系pH对针铁矿 (G)吸附Cd2+的影响与机制以及电解质 (KNO3)浓度对针铁矿、草酸化针铁矿 (G+40 )吸附Cd2+的影响差别及原因。结果表明 ,低浓度草酸 (1mmolL-1 )促进Cd2+的吸附 ;高浓度草酸 (1mmolL-1/sup )抑制Cd2+的吸附。已吸附在针铁矿表面的草酸对Cd2+ 吸附的影响与液相中草酸的影响不同 ,这主要与草酸引起的针铁矿表面电荷性质的变化、草酸在固液两相间的分配、草酸与Cd2+的配合作用和竞争作用有关。电解质 (KNO3)浓度对针铁矿和草酸化针铁矿吸附Cd2+的影响明显不同 ,随KNO3 浓度的提高 ,针铁矿的Cd吸附率由 44.5%增至 95%以上 ,而草酸化针铁矿吸附率由 29%降至6.2% ,这主要决定于二者的电荷零点 (PZC)和体系pH变化的不同。

Effects and mechanisms of oxalate on Cd(II) adsorbed on goethite at different pH and electrolyte concentration

The effects and mechanisms of oxalate on Cd(II) adsorbed by goethite at different oxalate concentration and pH in tested systems as well as the differences and reasons of the influence on Cd(II) adsorbed by goethite and by oxalated goethite were studied The results showed that oxalate in low concentration (<1mmol·L^-1) promoted Cd sorption whereas oxalate in higher concentration (>1mmol·L^-1) restrained Cd sorption There were some differences of the influence resulted from the oxalate which had been adsorbed by the goethite and the oxalate in the liquid phase It was mainly in relation to those, such as 1) the change of the surface charge characters was resulted from the oxalate sorption on goethite, 2) the oxalate distribution between solid phase and liquid phase, 3) the complexation and competition between oxalate and Cd 2+ The influence of electrolyte (KNO₃) on Cd²⁺ adsorbed by goethite(G) and by oxalated goethite (G+40) was different obviously The Cd²⁺ sorption rates of goethite increased from 44.5% to 95% over with the increase of the electrolyte concentration whereas the Cd²⁺ sorption rate of oxalated goethite(G+40) decreased from 29% to 6.2% These were primarily dependent on the differences of their PZC and pH in tested systems