可变电荷土壤和矿物Pb2+ and Cu2+吸附动力学: Ⅶ. Pb2+吸附后H+释放的动力学

The kinetics of H⁺ releasing after Pb²⁺ adsorption was studied by the potentiometric method combined with the acid-base titration curve technique. Results showed that pH of latosol, red soil and kaolinite suspensions dropped sharply, and then decreased gradually. Most of the H⁺ exchanged, more than 60%, was displaced at the first minute after Pb²⁺ was added into the suspension. More H⁺ was released at a higher concentration of Pb²⁺ added for a given sample and the amount of H⁺ released decreased in the order of red soil > latosol > kaolinite at a given concentration. The time-dependent data of H⁺ releasing of latosol, red soil and kaolinite at two concentrations could be fitted best with the second-order equation among the six equations, including second-order equation, two-constant equation, Elovich equation, parabolic diffusion equation, first-order equation and exponential equation. The H⁺/Pb²⁺ exchange stoichiometry increased with time, and a stable ratio of H⁺/Pb²⁺, being 1.73, 1.92 and 2.01 for kaolinite, latosol and red soil, respectively, was reached 25 minutes later.