Over the last several decades, a variety of methods have been developed for treating contaminated sites. Which technique is applied depends on the type of contaminant, the extent of dispersion, and the likelihood of additional contamination during the cleanup. Among the selection of potential techniques is the artificial freezing method, in which soil is frozen to significantly lower the permeability and prevent further diffusion of pollutants. While this method appears to have merit in theory, few studies have investigated the migration of pollutants during the soil freezing process. In this paper, a series of artificial freezing purification tests were performed and the influences of different freezing rates on purification efficiency were investigated. The experimental results show that the freezing rate is an important factor affecting the freezing purification efficiency for heavy metal copper and the purification rate decreases rapidly with increasing freezing rate. A soil freezing rate of 0.3 °C/h results in a heavy metal copper purification rate of only 27%; far less than that of the freezing rate of 0.05 °C/h, where the purification rate is 85%. This study demonstrates that a strong correlation exists between the purification rate of heavy metal copper and the soil freezing rates. We also demonstrate that the purification rate can be expressed as a cubic of the soil freezing rate. Therefore, the optimal purification of contaminated sites can be obtained by determining the proper freezing rate.