PubMed · 5408945
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E Skog, J E Wahlberg. 1969. Patch testing with potassium dichromate in different vehicles.. https://pubmed.ncbi.nlm.nih.gov/5408945/
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Fluidized zero valent iron (ZVI) process was conducted to reduce hexavalent chromium (chromate, CrO(4)(2-)) to trivalent chromium (Cr(3+)) from electroplating wastewater due to the following reasons: (1) Extremely low pH (1-2) for the electroplating wastewater favoring the ZVI reaction. (2) The ferric ion, produced from the reaction of Cr(VI) and ZVI, can act as a coagulant to assist the precipitation of Cr(OH)(3(s)) to save the coagulant cost. (3) Higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. For influent chromate concentration of 418 mg/L as Cr(6+), pH 2 and ZVI dosage of 3g (41 g/L), chromate removal was only 29% with hydraulic detention time (HRT) of 1.2 min, but was increased to 99.9% by either increasing HRT to 5.6 min or adjusting pH to 1.5. For iron species at pH 2 and HRT of 1.2 min, Fe(3+) was more thermodynamically stable since oxidizing agent chromate was present. However, if pH was adjusted to 1.5 or 1, where chromate was completely removed, high Fe(2+) but very low Fe(3+) was present. It can be explained that ZVI reacted with chromate to produce Fe(2+) first and the presence of chromate would keep converting Fe(2+) to Fe(3+). Therefore, Fe(2+) is an indicator for complete reduction from Cr(VI) to Cr(III). X-ray diffraction (XRD) was conducted to exam the remained species at pH 2. ZVI, iron oxide and iron sulfide were observed, indicating the formation of iron oxide or iron sulfide could stop the chromate reduction reaction.
A framework for the evaluation of leaching behavior of inorganic constituents from stabilized/solidified refinery oily sludge and ash produced from incineration of oily sludge with cement was employed. Metal and anion release as a function of pH was investigated. The leaching test consisted of multiple parallel extractions at pH range from 2 to 12. Remarkably good immobilization >98% was observed for metals of solidified ash at pH>6 and >93% of solidified oily sludge at pH>7. Sulfate leaching was high at pH range 2-12. The leaching behavior of metals and anions was simulated by VMINTEQ. The calculations showed that leaching behavior of Zn, Ni and Cu was controlled by chemical equilibrium and surface complexation onto ferrihydrite, at the pH range 2-12. The dominant solid phases that controlled metal leachability were metal hydroxides. The dominant mechanism that described sulfate leaching was found to be chemical equilibrium. Sulfate and also chromate leachability was controlled by Ettringite and Cr(VI)Ettringite as the major minerals affecting their release.
A simple and efficient microemulsion-based technique, which used the new Tx-100/cyclohexanol/ H2O system, was developed to synthesize SrCrO4 nanowire based nanostructures, including nanowire bundles and flower-like structures at different temperature. X-ray powder diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to characterize the products. Studies found that the reaction temperatures and the reaction systems have great influences on the final products. Optical properties studies by UV-Vis spectra and photoluminescence (PL) spectra confirmed that the as-obtained nanowires showed distinct optical activity under UV and visible light irradiation.