pH对不同来源腐殖酸吸附铅和锰的影响

笔者以从草碳、褐煤和风化煤中提取的腐殖酸为供试材料，研究了三种来源腐殖酸对Pb2+和Mn2+的吸附率在不同pH值条件下的变化规律。结果表明，pH显著影响腐殖酸与Pb2+和Mn2+的络合反应。三种来源腐殖酸对Pb2+和Mn2+的吸附率均以pH3.5时为最低，随着pH值的增大，三种来源腐殖酸对Pb2+和Mn2+的吸附率均有不同程度的增高；当pH>5.5时，Pb2+和Mn2+的吸附率随pH值的变化较为平缓。pH值的变化对Mn2+和三种来源腐殖酸上的络合反应影响较大，由吸附率由pH3.5时的24%增加至pH5.5时的83%，增加了近2.5倍；而pH从3.5增大到4.5时，Pb2+的吸附率仅增加了约25%。与对照相比，pH3.5～5.5时，腐殖酸能够降低溶液中Pb2+的浓度，pH4.5～6.5时，降低Mn2+的浓度，从而降低该条件下这两种金属离子的生物有效性。

Effect of pH on the Adsorption of Pb2+ and Mn2+ on Humic Acids from Three Different Sources

The humic acids were extracted from peat, lignite and weathering coal, respectively, to study the effect of pH on the adsorption of Pb2+ and Mn2+ on them. The adsorption percentage was used reflect the characteristics of reaction between the two metal irons and three types of humic acids at pH 3.5-7.5. The results showed that the adsorption of both metal irons on three types of humic acids was affected by pH significantly. The lowest adsorption percentage of Pb2+ and Mn2+ was found at pH 3.5. The adsorption percent of both two metal irons on three types of humic acids increased with the increase of pH value, whereas, when pH value was larger than 5.5, the change of adsorption percent of two metal irons became insignificant. The effect of pH on the adsorption percentage of Mn2+ was much more significant than that on Pb2+, for example, the adsorption percentage of Mn2+ increased 2.5 fold from 24% at pH 3.5 to 83% at pH 5.5, while the one of Pb2+ increased by 25% from pH 3.5 to 4.5. Comparing with the control, the content of Pb2+ (pH3.5-5.5) and Mn2+ (pH4.5-6.5) in the solution increased with humic acids addition. The results suggested that the availability of two metal irons for plant was reduced in that condition.