Lead-contaminatedsoils Stabilized by Modified Thomas Phosphate

The Thomas phosphate (TP) is extensively used in heavy metal-contaminated soils stabilization. However, the low solubility of TP has negative effects on stabilizing heavy metal-contaminated clay. In order to improve the solubility of TP, TP was modified by different acid, different concentration and curing age. Then, two kinds of modified TP were screened, and the restoration effect of lead contaminated soil was studied. The TCLPs of Pb-contaminated clay stabilized by selected acid modified TP with curing 7 days and 28 days were studied. The designed concentrations of Pb were 500, 2 000, and 5 000 mg/kg (by dry weight), and the TP contents were from 3% to 35%. The results indicate that acetic acid modified TP and nitric acid modified TP have superior characteristics compared to other modified TP.They have the greater pH value and calcium dissolved content (Ca), and lower electrical resistivity value. Furthermore, when the Pb concentration is no more than 2 000 mg/kg, both acetic acid modified TP and nitric acid modified TP can satisfy the requirement of US EPA. When the Pb concentration is 5 000 mg/kg, the parents TP cannot stabilize the Pb-contaminated clay enough to satisfy the standard, and the additive stabilizer should be considered in order to improving the effects of stabilization.