Influence of leaching conditions on the release kinetics of lead, chromium and nickel from solidified/stabilized cementitious materials

Stabilization/solidification and recycling of sediment from Taihu Lake in China: Engineering behavior and environmental impact

Investigations of stabilized/solidified sediment (S/S sediment) by simulated field-construction processes (crushing and filling) are fundamental to evaluating the potential reuse as fill materials. A series of tests were conducted on the samples prepared from S/S sediment grains (SG), which was obtained by crushing the cement treated sediment. By sampling the SG with different field-curing durations (t1: 28, 35, 56 and 98 days) and measuring them by unconfined compressive strength (UCS) tests, the effect of t1 on the UCS was investigated. By continually curing the samples prepared from the SG with 28 field-curing days in laboratory for an additional 7, 28, 35 and 70 days (t2) and subjecting them to UCS and tank leaching tests with different ambient (leachate) pH values (1, 4, 7, 10 and 14), the effect of t2 and ambient pH was evaluated. Increasing t1 and t2 was found to significantly influence the strength of SG, which highlights the importance of an appropriate curing period. The releases of the metals (As, Cr, Cu, Zn, Pb, Ni, and Hg) in the SG exhibited a strongly pH-dependence but less correlation with t2. Neutral conditions (pH = 7) offered the best immobilization capacity for Cu; As, Cr, Ni and Zn exhibited the lowest release at pH = 10; the release of Pb decreased moderately with increasing pH. The S/S sediment complied with the acceptance criteria in terms of metal release and can be regarded as an environmentally friendly fill material. The results highlight the technical feasibility of stabilized sediment recycling in aquatic environment projects.

Treatment and remediation by the stabilization/solidification process based on hydraulic binders of soil contaminated by heavy metals

Nature and the environment are affected by various human industrial and/or urban discharges. Remediation for this problem requires first and foremost an in-depth analysis and an overall characterization of the intrinsic properties of the pollution-receiving environments. Secondly it is necessary to predict in these environments the behavior of dangerous chemical species (here particularly heavy metals) in the long term. This study focuses mainly on a detailed characterization of 4 soil samples sampled in vicinity of wild dump-BOULIMAT located 15 km west of the city of Bejaia-Algeria. The samples were characterised by atomic absorption spectrometry, X-ray diffraction, Fluorescence X and Infrared spectroscopy. The data showed high concentrations of metallic elements especially Zn (2,651.8 mg.kg−1) and Ni (163.44 mg.kg−1) in the soil samples. For their remediation, the stabilization/solidification (S/S) process with hydraulic binders appeared promising in reducing the polluting power of metal. This approach has considerably reduced the content of pollutants; 98 % removal was obtained for Ni and 99 % for Zn. The XRD analysis technique revealed the occurrence or absence of metallic elements in the crystallized phases.

Behavior of metallic trace elements containing in stabilized and solidified oily petroleum sludge

The present work examines the influence of the leaching conditions on the release of various chemical elements from a cementitious material obtained by solidification of an industrial waste rejection of Algeria. Toxicity Characteristic Leaching Procedure (TCLP), X-ray diffraction (XRD) and Scanning electron microscopy coupled with energy dispersive X-ray microanalysis SEM-EDX analyses were employed to characterize the waste and the stabilized/solidified materials. Than several formulations were prepared with different percent of waste ranging from 0 % to 30 %. To evaluate the influence of leaching conditions on the release of chemical ions (Zn2+, Pb2+, Cl-, Mg2+, Ca2+, Na+, K+ and SO42−) contained in the stabilized and solidified materials, the Acid Neutralization Capacity (ANC), the Pore Water (PW) and Monolith Leaching Tests (MLT) have been carried out. The leaching tests (ANC, PW and MLT) have shown a low metal leachability. However, the lowest released amount was observed for the MLT.

Stabilization/solidification by hydraulic binders of metal elements from landfill leachate

The objective of this work is to use stabilization/solidification (S/S) on the landfill leachates that often are heavily polluted by heavy metals and require proper treatment before discharge into the environment. The process consists of a S/S using a hydraulic binder in order to limit the solubility and mobility of the pollutants. While cement is the most used binder based on S/S values, in this study we substituted it by cement kiln dust (CKD) in two replacement ratios 25.50 and 100 %. The resulting effect on mechanical resistance and on retention of pollutants was evaluated. A metal (lead, iron and zinc) contaminated leachate from the landfill site of Sidi-Bouderham in Algeria was mixed with an amount of cement and cement kiln dust in different proportions in order to optimize our formulations. The smooth paste was obtained and a standardized test of the test specimens was analyzed for mechanical resistance after 7 and 28 d of setting. Our results show that F1P (100 % Cement) and F2P (75 % Cement + 25 % CKD) point on satisfactory mechanical strength and metal retention capacity. Our approach suggests a promising approach for remediation of polluted sites.