Recovery of Cr(III) by using chars from the co-gasification of agriculture and forestry wastes

Godinho, Delfina; Nogueira, Miguel; Bernardo, Maria; Dias, Diogo; Lapa, Nuno; Fonseca, Isabel; Pinto, Filomena

Recovery of Cr(III) by using chars from the co-gasification of agriculture and forestry wastes

2019

The aim of the present work was to assess the efficiency of biochars obtained from the co-gasification of blends of rice husk + corn cob (biochar 50CC) and rice husk + eucalyptus stumps (biochar 50ES), as potential renewable low-cost adsorbents for Cr(III) recovery from wastewaters. The two gasification biochars presented a weak porous structure (ABET = 63–144 m² g⁻¹), but a strong alkaline character, promoted by a high content of mineral matter (59.8% w/w of ashes for 50CC biochar and 81.9% w/w for 50ES biochar). The biochars were used for Cr(III) recovery from synthetic solutions by varying the initial pH value (3, 4, and 5), liquid/solid (L/S) ratio (100–500 mL g⁻¹), contact time (1–120 h), and initial Cr(III) concentration (10–150 mg L⁻¹). High Cr(III) removal percentages (around 100%) were obtained for both biochars, due to Cr precipitation, at low L/S ratios (100 and 200 mL g⁻¹), for the initial pH 5 and initial Cr concentration of 50 mg L⁻¹. Under the experimental conditions in which other removal mechanisms rather than precipitation occurred, a higher removal percentage (49.9%) and the highest uptake capacity (6.87 mg g⁻¹) were registered for 50CC biochar. In the equilibrium, 50ES biochar presented a Cr(III) removal percentage of 27% with a maximum uptake capacity of 2.58 mg g⁻¹. The better performance on Cr(III) recovery for the biochar 50CC was attributed to its better textural properties, as well as its higher cation exchange capacity.

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