Removal of copper from sulfate solutions using biochar derived from crab processing by-product. (1st February 2022)

• Record Type: Journal Article
• Authors: Hopkins, David T.; MacQuarrie, Stephanie; Hawboldt, Kelly A.
• Is Part Of: Journal of environmental management. Volume 303(2022)
• Publication Date: 2022-02-01
• Subjects: Acid mine drainage -- Adsorption -- Biochar -- Copper -- Crab shell -- Pyrolysis; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2021.114270
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Increasing metal demand is accelerating the mining and processing of minerals, however to ensure sustainable growth innovative approaches are required to better manage associated effluents. Biochar from the fast pyrolysis of residues from fishery and forestry operations has been studied as a low-cost, environmentally and economically friendly method for treating mine tailings and processing effluents. However, the bulk of the studies focus on terrestrial biomass (e.g. wood) and do not include potential inhibition/enhancement of adsorption due to pH controlling compounds. In this work biochar generated from snow crab (Chionoecetes Opilio) processing was studied as an adsorbent for copper solutions containing sulfate (a key compound in sulfide ore mining waters) with the objective of assessing adsorption capacity and the impact of sulfate on copper adsorption. The biochar, a porous structure comprised of calcite (CaCO3 ), was alkaline and has a negative zeta potential under neutral and basic conditions. The crab biochar removed over 99% of Cu 2+ from a 100 mg/L solution (sourced as CuSO4 ) at a dosage of 5 g/L, which was higher than lignocellulosic biochar at the same biochar dosage. While metal adsorption can often be impacted at acidic conditions, Cu 2+ adsorption was not impacted by initial acidic pH due to the biochar's buffering capacity. The Pseudo-Second Order (PSO) model fit the adsorption rate with maximum adsorption achieved in approximately 2 h. The maximum adsorption isotherm capacity was 184.8 ± 10.2 mg/g for Cu 2+, much higher than existing commercial activated carbons and previously studied lignocellulosic biochars and followed the Freundlich isotherm. The adsorption mechanism responsible for removal of Cu 2+ was found to be precipitation, in the form of the mineral posnjakite (Cu4 [(OH)6 SO4 ]·H2 O). These results indicate for the first time that crab-based biochars are capable of adsorbing large quantities of Cu 2+ from sulfate-rich solution, while also buffering solution pH, demonstrating promise as an acid mine drainage treatment for removal of harmful metals and reduction of acidity. Highlights: Crab processing waste was pyrolyzed at 500 °C to produce Crab Shell Biochar (CSB). CSB was rich in calcite (CaCO3 ) and strongly alkaline (pH = 11.75). CSB adsorbed Cu 2+ well across a range of pH due to buffering capacity. Adsorption capacity for Cu 2+ was 184.8 mg/g, outperforming commercial adsorbents. Cu 2+ was adsorbed mainly through precipitation as posnjakite (Cu4 [(OH)6 SO4 ]·H2 O).