Reduction of Hexavalent Chromium By Agave Biochar and Modified Biochar.

Reduction of hexavalent chromium by Agave biochar and modified biochar

Soil pollution can severely affects ecosystems involving groundwater and rivers by industrial wastes containing heavy metals. Hexavalent chromium (Cr(VI)) is a very toxic element for living organism, and has been discharged to ecosystem from industrial plants. In Guanajuato, Mexico, soil pollution caused by Cr(VI) has been a serious problem due to increasing industrial production. Lignocellulose materials contained in timber and fiber are known to adsorb and reduce Cr(VI). Bagasse of agave plant (Agave tequilana) from which tequila is produced is one of examples of lignocellulose materials. In addition, reduction potential will be improved by lignocellulose materials when pyrolysed from 200°C to 500°C called biochar (BC). The objective of this study was to understand the mechanism of adsorption and reduction for Cr(VI) by agave bagasse (AB) and its BC.

Agave bagasse was collected from a tequila factory in Guanajuato, dried in an oven for 24 h at 108°C. The BC was produced from AB for 1 h at temperatures of 400°C and 800°C (<150 µm) under oxygen-limited conditions. The modified BCs were prepared after treating BCs with H­₂O₂ (15% w/w) and nanoscale zero-valent iron (nZVI) treatment. H₂O₂ treatment was done by stirring 1 g BCs biochar in 20 mL solution for 2 h. To prepare BC with nZVI, BC was dissolved in FeO₄·7H₂O solution and stirred for 60 min under anaerobic conditions. Then, BC particles with nZVI were synthesized by addition of NaBH₄solution.

Batch experiment was performed by mixing previously N₂-purged 100 mg Cr(VI) L^-1 K₂Cr₂O₇ solution and 0.1 or 0.5 g L^-1 of AB or each biochar samples stirred in 800 mL glass container. ORP and pH of the solution were measured at every 1 min for 90 min. Total Cr, Cr(VI), and Cr(III) were measured in sub-sample solution collected at total of 10 time series.