Influence of pH on the compressibility of zinc-contaminated kaolin and the zinc diffusion characteristics

To examine the effect of zinc ion on the compressive property of the saturated kaolin and the diffusion characteristics of zinc ion under different pH values, a series of one-dimensional consolidation tests and soil column diffusion tests were carried out with artificially prepared remolded soil samples. The test results indicate that the compressibility index of zinc-contaminated kaolin does not change much if the concentration of zinc ion is lower than 0 05 mol/L. However, the increase of precipitation of Zn(OH)2 will lead to a slight decrease in soil compressibility. The decreasing velocity of the zinc ion in the free solution is the highest over the alkaline kaolin, then the neutral kaolin, and lowest over the acid kaolin. The electrical conductivity (EC) of the solution can indirectly reflect the concentration of dissolved zinc ion. When the kaolin is in neutral and alkaline environments, the EC of the free solution above the soil column is positively correlated with the concentration of zinc ion in the solution. But if the kaolin is in an acidic environment, the conductivity of the free solution above the soil column is negatively correlated with the concentration of zinc ion. Such an opposite variation under different pH value of soils should be paid more attention to.