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Characterization of the Cr(VI)/Cr(III) Ratio in Aerosols
Published in Jacques Buffle, Herman P. van Leeuwen, Environmental Particles, 2019
Rob F.M.J. Cleven, Jan L.M. deBoer, Anton van der Meulen
Under environmental conditions chromium in compounds exists in the trivalent Cr(III) or the hexavalent Cr(VI) state. Cr(III) is an essential trace element for mammals, including man, whereas it is presumed that Cr(VI) compounds are genotoxic and potentially carcinogenic in humans.1 Evidence exists for the carcinogenicity of calcium chromate, strontium chromate, and zinc chromate. In the diet, chromium is predominantly present as Cr(III). Cr(VI) present in the diet will be converted partially to Cr(III) due to intragastric reduction. There is sufficient evidence, based on animal studies, that exposure to Cr(VI) compounds by inhalation will result in an increased risk for carcinogenic effects.2 The unit risk for Cr(VI) is 40.10−3.1 This means that in a hypothetical population of 1000, in which all individuals are exposed continuously from birth throughout their lifetimes to a concentration of 1 μg.m−3 of hexavalent chromium in the air they breathe, 40 additional cases of cancer are expected to occur. Assuming an acceptable risk of one extra case of cancer per million persons exposed lifetime, this risk corresponds with an airborne concentration of 0.025 ng Cr(VI).m−3. Many people will be exposed to unacceptable chromium levels, if all airborne chromium would be in the hexavalent state, as concentrations of total Cr in ambient air amount to some ng.m−3. Thus, there exists a need for speciation techniques to measure airborne Cr(VI).
Dissolved Matter
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
The amount of a substance required to saturate 100 g of water at a given temperature is called the solubility of that substance at that temperature. Changes in temperature always change the solubility of a solute. As a rule, solids are more soluble in hot than in cold water, although occasionally the reverse is true. Some compounds of calcium, such as calcium hydroxide, Ca(OH)2, and calcium chromate, CaCrO4, belong to the latter group. The solubility of sodium chloride is only slightly affected by a change in temperature.
Citric-acid preacidification enhanced electrokinetic remediation for removal of chromium from chromium-residue-contaminated soil
Published in Environmental Technology, 2018
Fansheng Meng, Hao Xue, Yeyao Wang, Binghui Zheng, Juling Wang
Chromate production in China is mainly the extraction of chromium from chromite and chromium compounds by using traditional high-temperature roasting-immersion-multiple evaporation and crystallization processes. Normally, there are 2.5 or even 3 tons of highly toxic chromium slag come out after each ton of chromate production. And the chromium slag contains 1–3% by weight water-soluble sodium chromate (Na2CrO4) and 1–1.5% by weight acid-soluble calcium chromate (CaCrO4), which has been listed by the International Cancer Research Agency as one of the substances that are carcinogenic in animals [1]. The toxicity of chromium residue mainly comes from the enhanced oxidative corrosion and damage caused by hexavalent chromium [Cr(VI)] toward the organisms [2]. As a result, the soil contamination problem caused by the long-term piling of chromium slag has drawn great attention in the soil pollution control in China.
Influence of Cr3+, Co2+ and Cu2+ on the formation of calcium silicates hydrates under hydrothermal conditions at 200 °C
Published in Journal of Asian Ceramic Societies, 2020
Tadas Dambrauskas, Inga Knabikaite, Anatolijus Eisinas, Kestutis Baltakys, Martin T. Palou
It was observed, all investigated metal ions were intercalated into the structure of synthesis products or formed compounds during the hydrothermal synthesis because after synthesis the metal ions concentration in liquid medium was lower than 0.01% under all experimental conditions. It was obtained that in the CaO-SiO2-Al2O3-Cr(NO3)3-H2O mixture, all chromium ions were intercalated to the structure of calcium silicate hydrates or formed amorphous structure compounds. It was determined, that after calcination of synthesis products with Cr3+ ions at 700°C temperature, calcium chromate was formed (CaCrO4).