Use of sulfuric acid-carbonization materials from grape pulp for the removal of hexavalent chromium (Cr(VI)): mechanism and characterization

Abstract

This study investigated the reduction of hexavalent chromium (Cr(VI)) with sulfur dioxide (SO₂) and adsorption of Cr(VI) onto dried grape pulp carbonized with sulfuric acid. Cr(VI) reduction capacities of SO₂ were determined. The filtrate was titrated with NaOH solution after shaking and filtering the carbonized material to retain unreacted sulfuric acid (H₂SO₄). Simple washing recovered 25–38% of the experimental acid at low concentrations. The carbonized material was washed twice with distilled water and then dried at 105 °C and weighed. The carbonized material had a yield of 56.6% (grape pulp/sulfuric acid ratios of 1:2), and the lower the H₂SO₄ content, the better the yield, suggesting that the higher the acid content, the lower the Cr(VI) content per unit grape pulp. Cr(VI) reduction capacities were 219.5, 195.3, and 190.9 mg Cr(VI)/g-H₂SO₄ for the grape pulp/sulfuric acid ratios of 1:1, 1:2, and 1:3, respectively.

Novelty statement: A carbonaceous material was obtained from grape pulp by carbonizing with concentrated sulfuric acid. The main objective of this study was to evaluate gas, liquid, and solid products or co-products obtained during carbonization process for hexavalent chromium treatment in aqueous solutions. In this context, (a) hexavalent chromium reduction capability of the gas evolved during carbonization was determined, (b) characterization of unreacted acid recovered by washing the carbonized product left after carbonization step was done, (c) carbonaceous adsorbent obtained was characterized and (d) hexavalent chromium adsorption characteristics of carbonaceous material obtained was determined.

HIGHLIGHTS

• Reduction and adsorption mechanisms of hexavalent chromium were investigated.

• A waste recycling method was proposed.

• The effects of sulfuric acid on carbonization were assessed.

• The structures and chemical compositions of a carbonized material were evaluated.

• The carbonized material is a cost-effective porous adsorbent for a clean environment.

Keywords:

• Cr(VI) adsorption-isotherm-kinetic-thermodynamic
• Cr(VI) reduction
• Grape pulp-carbonization-carbon