Systematic study on the reduction efficiency of ascorbic acid and thiourea on selenate and selenite at high and trace concentrations.

Author(s) Zhang, G.; Gomez, M.Alberto; Yao, S.; Ma, X.; Li, S.; Cao, X.; Zang, S.; Jia, Y.
Journal Environ Sci Pollut Res Int
Date Published 2019 Apr

Selenate (Se(VI)) and selenite (Se(IV)) are common soluble wastewater pollutants in natural and anthropogenic systems. We evaluated the reduction efficiency and removal of low (0.02 and 2 mg/L) and high (20 and 200 mg/L) Se(IV) and Se(VI) concentrations to elemental (Se) via the use of ascorbic acid (AA), thiourea (TH), and a 50-50% mixture. The reduction efficiency of AA with Se(IV) to nano- and micro-crystalline Se was ≥ 95%, but ≤ 5% of Se(VI) was reduced to Se(IV) with no Se. Thiourea was able to reduce ≤ 75% of Se(IV) to bulk Se at lower concentrations but was more effective (≥ 90%) at higher concentrations. Reduction of Se(VI)→Se (IV) with TH was ≤ 75% at trace concentrations which steadily declined as the concentrations increased, and the products formed were elemental sulfur (S) and SSe phases. The reduction efficiency of Se(IV) to bulk Se upon the addition of AA+TH was ≤ 81% at low concentrations and ≥ 90% at higher concentrations. An inverse relation to what was observed with Se(IV) was found upon the addition of AA+TH with Se(VI). At low Se(VI) concentrations, AA+TH was able to reduce more effectively (≤ 61%) Se(VI)→Se(IV)→Se, while at higher concentrations, it was ineffective (≤ 11%) and Se, S, and SSe formed. This work helps to guide the removal, reduction effectiveness, and products formed from AA, TH, and a 50-50% mixture on Se(IV) and Se(VI) to Se under acidic conditions and environmentally relevant concentrations possibly found in acidic natural waters, hydrometallurgical chloride processing operations, and acid mine drainage/acid rock drainage tailings. Graphical Abstract ᅟ.

DOI 10.1007/s11356-019-04383-z
Keywords Ascorbic Acid; Mining; Models, Chemical; Oxidation-Reduction; Selenic Acid; Selenious Acid; Selenium; Selenium Compounds; Sulfur; Thiourea
ISSN 1614-7499
Citation Environ Sci Pollut Res Int. 2019;26(10):1015910173.

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