Speciation analysis of chromium after reduction of chromium (VI) by humic acid

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Chromium species after the reduction of Cr(VI) by humic acid (HA) were analyzed. Cr(VI) inorganic species were determined by a colorimetric method with diphenylcarbazide, and inorganic Cr(III) cationic and Cr(III)‐HA complex species were determined by atomic absorption spectrom‐etry after separation with a cation‐exchanger. After the reduction of Cr(VI) by HA for 62 days, about 30 % of the total Cr existed in the Cr(III) complex bound with HA, and about 10 % of the total Cr was present as the inorganic Cr(III) form. The ratio of the concentration of Cr(III)‐HA complex to reduced species of Cr(VI) increased with pH. It was found that the majority of chromium species after the reduction was present as complex form with HA. The results of the time‐dependent speciation analysis showed that the concentration of inorganic Cr(III) cation dissociated from Cr(III)‐HA complex increased with the reaction time in the acidified condition. The fate and hazardous of Cr species after the reduction were discussed by referring to the obtained kinetic results.