Comparing the Efficacy Rates of Lime and Poly Aluminum Chloride Coagulants in Cadmium Removal from the Landfill Leachate by Chemical Precipitation

Aims: Chemical precipitation is a simple, efficient, and cost-effective method for eliminating heavy metals found in landfill leachate. The aim of the present study was to compare the efficacy rates of cadmium removal with the coagulants like poly aluminum chloride and lime using chemical precipitation method.
In this experimental study, the raw studied samples were collected from the landfill located in Kahrizak, Iran, in May 2014. The elimination rates of cadmium at 1000, 1500 and 2000mg/l concentrations of lime; at 100, 150 200mg/l concentrations of poly aluminum chloride; at 7, 9, 11 pH levels; and during 20, 40 and 60min of the reaction time were studied. Data were analyzed in SPSS 16 software using ANOVA, independent T and repeated measurement tests.
Findings: The maximum elimination rate of cadmium in both lime and poly aluminum chloride were seen at pH=11. The maximum rates of cadmium removal occurred at minute 40 in 2000mg/l concentration of lime (99.4%) and 200mg/l concentration of poly aluminum chloride (98%).
Both lime and poly aluminum chloride have the best cadmium removal rate from leachate at pH=11 after 40 minutes of precipitation process. Being more inexpensive and easily available than poly aluminum chloride, lime is considered as an appropriate coagulant.