Abstract:

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.