Experimental study on freezing temperature and its influencing factors of loess contaminated by heavy metals

Abstract

This paper attempts to reveal the freezing temperature and its influencing factors of heavy metal-contaminated loess by adopting two cooling methods: fast and slow grading. As a result, Lanzhou loess was used as an experimental material to make polluted soil with varying heavy metal concentrations and initial water content. The pollutant elements included Zn, Ni, Cu, Cr, Cd, and Pb. The findings demonstrate that: 1) The slow cooling rate causes supercooling, jumping, and a progressive decrease in the temperature of the polluted soil. Different cooling methods have no obvious effect on freezing temperature. Furthermore, the freezing temperature of contaminated soil varies depending on its water content. The impact of increasing water content on freezing temperature is not evident; 2) The freezing temperature of loess decreases with the increase of heavy metal ion content. The freezing temperature of loess polluted by Zn, Ni and Cd ions decreased linearly with the increase of ion content. The influence of cations on the freezing temperature of loess is as follows: Zn2+> Ni2+> Cd2+> Cr3+> Pb2+> Cu2+. The influence order of anions is Cl− > SO42−; 3) The freezing temperature of loess containing heavy metal ions is about equal to the freezing temperature of the corresponding heavy metal solution plus the freezing temperature of loess itself. The freezing temperature of heavy metal-polluted loess follows the temperature superposition principle.