Effects of pH on leaching behavior of compacted cement solidified/stabilized lead contaminated soil

Abstract

The compacted cement stabilized/solidified (S/S) metal contaminated soil could be used for “controlled utilization,” such as road base, quarry rehabilitation, and lagoon closure. However, the complexity and variability of environment, especially the acid rain and alkaline leachate, greatly influence the leaching behaviors of S/S heavy metal contaminated soil and threaten the environment. The leaching characteristics of the compacted S/S samples were investigated over a wide range of pH (2.65, 3.65, 5.00, 7.00, and 10.00). Semidynamic leaching tests were conducted to evaluate the effects of pH on effectiveness and controlling leaching mechanism of compacted cement S/S treated lead (Pb) contaminated soil. Results showed that there was no obviously change of the cumulative fraction of Pb leached (CFL) in weak acid or weak alkaline conditions (pH ranging from 5.00 to 10.00), and the strong acid significantly altered the leaching behaviors of Pb. The calculated values of effective diffusion coefficient (De) and leachability index (LX) indicated that the mobility of Pb2+ was weak and the compacted S/S treatment could be used for “controlled utilization” with environment pH value ranging from 3.65 to 10.00. Especially, the LX value was 8.49 when the compacted S/S sample was immersed in the leachant with pH 2.65, indicated that the S/S sample was not considered appropriate for disposal. The mechanism controlling Pb2+ leaching from S/S samples at all the pH range (2.65–10.00) appeared to be diffusion, and with pH decreasing in acid conditions, the controlling leaching mechanism somehow was changing from diffusion to surface wash‐off. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 149–155, 2016