Variance in heavy metal leachability of Pb-, Ni-, and Cr-contaminated soils through red brick sintering procedure.

The technology for remediating heavy metal-contaminated soil is considerably limited because heavy metals do not undergo decomposition. Off-site reuse has emerged as the main technique for treating heavy metal-contaminated soil. Soil is the primary material in red brick making; and in the sintering procedure, heavy metals could solidify and stabilize within bricks. In this study, lead-, nickel-, and chromium-contaminated soils were collected from multiple agricultural fields. The sintering process was performed using a kiln that was for making red bricks. The sintering temperature was approximately 1000 °C. Soil and brick samples, before and after sintering, were analyzed for metal extraction concentration and binding form distribution. After sintering, the concentrations of Pb, Ni, and Cr determined through X-ray fluorescence approximated the concentrations in the soil. However, in the bricks, the bioavailability concentration of Pb, Ni, and Cr is less than 1% of that in the soil; the toxicity characteristic leaching procedure (TCLP) leaching concentration of Pb in the bricks was only 4% of that in the soil, and the leaching concentrations of Ni and Cr were lower than the detectable concentration. For the aqua regia extraction method, in the bricks, the Pb, Ni, and Cr were extracted and the concentrations accounted for 4.6%, 8.8%, and 9.4% of the concentrations in the soil, respectively. After sintering, more than 95% of Ni and Cr in the bricks were in residual fractions. The sintering process has the ability to stabilize the heavy metals in the contaminated soil.

Composition and source apportionment of PAHs in sediments at river mouths and channel in Kaohsiung Harbor, Taiwan.

Fifty-eight sediment samples were collected in 2009 from the bottom of river mouths near Kaohsiung Harbor (Taiwan) and the harbor channel for the analyses of polycyclic aromatic hydrocarbons (PAHs) using gas chromatography-mass spectrometry (GC-MS). Concentrations of total PAHs varied from 39 to 30,521 ng g(-1) (dry weight); samples collected from the mouths of Love River, Canon River, Jen-Gen River, and Salt River showed the highest PAHs concentrations. This indicates that the major sources of sediment PAHs come from those polluted urban rivers and the harbor channel. In samples collected from the Salt River mouth, approximately 43% of the PAHs are identified as PAHs with 2 or 3 rings. However, samples collected from other locations contain predominantly PAHs with 4 rings (32 to 42%) or 5 and 6 rings (36 to 44%). Emissions from traffic-related sources and waste incineration contribute to the majority of PAHs found in most channel and river mouth sediments. However, coal/oil combustion is the main cause of high concentrations of PAHs observed in the Salt River mouth sediments. Principal component analyses with multivariate linear regression (PCA/MLR) have been used to further quantify the source contributions, and the results show that the contributions of coal/oil combustion, traffic-related and waste incineration are 37%, 33% and 30%, respectively.

Remediation of soils contaminated with chromium using citric and hydrochloric acids: the role of chromium fractionation in chromium leaching.

Acid washing is a common method for soil remediation, but is not always efficient for chromium-contaminated soil. Both soil particle size and the forms of chromium existing in the soil affect the efficiency of soil washing. Laboratory batch and column dissolution experiments were conducted to determine the efficiencies of citric and hydrochloric acids as agents to extract chromium from soils contaminated with chromium. The effects of soil particle size and chromium fractionation on Cr leaching were also investigated. About 90% of chromium in the studied soil existed either in residual form or bound to iron and manganese oxides, and Cr fraction distributions were similar for all soil particle sizes. Almost all exchangeable and carbonate-bound chromium was removed by washing once with 0.5 M HCl, whereas organic chromium was more effectively removed by washing with citric acid rather than with HCl solution of the same concentration. For chromium fractions that were either bound to Fe-Mn oxides or existed as residual forms, the efficiencies of acid washing were usually 20% or less, except for 0.5 M HCl solution, which had much higher efficiencies. Separation of the soil sample by particle size before the separate washing of the soil fractions had little improvement on the chromium removal.