紫色土吸附Cu2+、Zn2+对水体中土壤颗粒凝聚沉降的影响

研究中性紫色土表面吸附Cu~(2+)、Zn~(2+)后对其在水体中凝聚沉降的影响,为重金属离子释放对三峡库区水-土界面生态系统造成的风险提供数据参考。2014年10月,采集西南大学桑园的中性紫色土表层土壤,以Cu-(NO_3)_2和Zn(NO_3)_2配制重金属离子,进行Cu~(2+)和Zn~(2+)对中性紫色土凝聚沉降实验、测定中性紫色土颗粒吸附Cu~(2+)和Zn~(2+)后zeta电位值。研究结果表明:(1)中性紫色土吸附Cu~(2+)、Zn~(2+)后水体中土壤颗粒含量随时间不断减小,并且呈先快速后缓慢减小的规律,在不同浓度条件下土壤颗粒含量变化规律表现差异较大,其临界浓度分别为0.3~0.5和0.5~0.7 mmol/L。(2)水体中中性紫色土颗粒平均沉降速率均随Cu~(2+)、Zn~(2+)浓度升高而增大,分别从1.01 cm/min增加到2.92和2.58 cm/min,表现为Cu~(2+)Zn~(2+);过程分为3个阶段:缓慢增加,快速增加和基本不变,平均沉降速率随浓度变化临界范围分别为0.3~0.5和0.5~0.7 mmol/L。(3)水体中中性紫色土颗粒zeta电位绝对值随Cu~(2+)、Zn~(2+)浓度升高而变小,同时表现为Ca~(2+)Zn~(2+)Cu~(2+),土壤颗粒吸附Ca~(2+)、Cu~(2+)和Zn~(2+)后zeta电位绝对值随浓度变化临界浓度范围分别为0.8、0.3~0.5和0.5~0.7 mmol/L。重金属离子吸附在中性紫色土表面减小zeta电位值和静电斥力,加速土壤颗粒凝聚沉降过程。

Effect of Cu2+and Zn2+ Adsorption on the Aggregation and Settling of Neutral Purple Soil Particles

Heavy metal pollution has become a global environmental problem, they would brought the serious ecological effects when the heavy metal ions entered the environmental systems of water and soils. When the heavy metal ions adsorption on soil surface, they would been result in large change of the surface charge properties and effect of the process of aggregation and settling of soil particles. So, we choose the Cu2+, Zn2+ that the concentrations of them in soil and water were much higher than other, and study the Cu2+, Zn2+ adsorption effect on aggregation and settling of the neutral purplish soil particles, the result showed that: (1) The percentage of soil particles in the neutral purplish soil suspension decreased with time when they adsorbed Cu2+, Zn2+, it rapidly decreased at first and then stabilized with time. There are significantly different in the percentage of soil particles at the different concentration of Cu2+ and Zn2+. The range of critical concentrations of Cu2+, Zn2+ were 0.3~ 0.5 mmol L-1and 0.5~ 0.7 mmol L-1, it obviously lower than the critical concentrations of Ca2+ (0.8 mmol L-1); (2) The average settling velocity of the neutral purplish soil particles increased with the concentration of Cu2+ and Zn2+, the value of them increased from 1.01 cm min-1 to 2.92 cm min-1 and 2.58 cm min-1 respectively. The process was divided into three stages: slow increase at first, and then rapid increase, almost remain unchanged at last; (3) The absolutely value of zeta potential of the neutral purplish soil particles decreased with the concentration of Cu2+ and Zn2+, it followed Ca2+ > Zn2+ > Cu2+.The range of critical concentrations of Ca2+, Cu2+, Zn2+ were 0.8 mmol L-1, 0.3~ 0.5 mmol L-1and 0.5~ 0.7 mmol L-1, there are the similar regularity the with percentage of soil particles and the average settling velocity in the neutral purplish soil suspension. The result showed that the main influence factor of aggregation and settling of soil particles is the electrostatic repulsion.