In this research, the effect of soil washing in the removal of chromium- and cadmium-contaminated sludge samples collected from Pond 2 of the Tehran Oil Refinery was investigated. These metals are considered as hazardous substances for human health and the environment. The carcinogenicity of chromate dust has been established for a long time. Cadmium is also a potential environmental toxicant. This study was carried out by collecting sludge samples from different locations in Pond 2. Soil washing was conducted to treat the samples. Chemical agents, such as acetic acid, ethylenediaminetetra acetic acid (EDTA) and hydrochloric acid, were used as washing solutions to remove chromium and cadmium from sludge samples. The results of this study indicated that the highest removal efficiencies from the sludge samples were achieved using a 0.3 M HCl solution with 82.69% and 74.47% for chromium and cadmium, respectively. EDTA (0.1 M) in the best condition extracted 66.81% of cadmium and 72.52% of chromium from the sludges. The lowest efficiency values for the samples, however, were achieved using 3 M acetic acid with 41.7% and 46.96% removals for cadmium and chromium, respectively. The analysis of washed sludge indicated that the heavy metals removal decreased in the order of 3 M acetic acid < 0.1 M EDTA<0.3 M HCl, thus hydrochloric acid appears to offer a greater potential as a washing agent in remediating the sludge samples.

In this study, Polycyclic Aromatic hydrocarbons (PAHs) contaminated soil were collected from Ray Petrochemical industry and treated by Solidification/Stabilization (S/S) which is an effective technique for reducing the leachability of contaminants in soils. Since organic compounds interfere with cement hydration process, S/S technology will have difficulties while trying to immobilize organic contaminants. The treatment process was conducted using Portland Cement (PC) as the main binder and Microsilica (MS) as an additive to improve the effect of PC in immobilization of organic contaminants. Specimens were divided in two groups with constant cement percentage of 25% and 35%. Each group were again divided to three subgroups with 0%, 4% and 8% of MS. The efficiency of using MS in leaching behaviour of S/S samples was assessed by toxicity characteristic leaching procedure (TCLP). Lowest leach percentage of 14.66% for total PAHs in the paste contained 25% of cement and 8% of MS were obtained. The results indicated that the presence of MS in cement pastes had positive effect on reduction in concentration of contaminant in leachate.