Adsorptive Characteristics and Influence Factors of Humic Acid on Lead in Soil

Adsorptive capacity and dynamics characteristics of humic acid on Pb2+ in soil are studied by using a lead ion selective electrode. Influence factors including pH, temperature and ionic strength in the solution were tested. The results showed that adsorptive capacity increased with the increase of pH or ionic strength of the solution, but decreased with the increase of temperature of the solution. It has been found that the adsorption was in accordance with Linear isothermal adsorption (the regression coefficient is 0.958 1 ～ 0.954 7 ), when pH of the solution was under 4.00, while that with Langmuir isothermal adsorption (the regression coefficient is 0.977 6 ～ 0.999 8  ), when pH of the solution is between 4.00 and 7.00. We also discovered that stability of Pb2+ - humic acid complex enhanced with the increase of pH value for the solution, but the increased pattern at pH4.0 obviously differed from that at 4.00≤ pH≤ 7.00. This may be suggested that there were different reaction mechanisms at the two pH sections. The average H+ released by humic acid with a Pb2+ was less than 1, and affected by both the temperature and ionic strength of the solution.