Heavy metal sorption in biosorbents – Using spent grain from the brewing industry

Abstract

The sorption properties of brewer's spent grain (BSG) were assessed in terms of its usefulness in removing heavy metals from solutions. The specific objectives of the investigation involved studying sorption equilibrium and kinetics, assessing the influence of other cations on sorption efficiency, and examining the possibility of bed regeneration. The studies were carried out in a static system, with a constant ratio of solution volume to biosorbent mass, and using a flow through system. The affinity of metal cations to BSG functional groups was established and increased in the series: Mn2+ ≈ Zn2+ < Ni2+ < Cd2+ < Cu2+ < Pb2+. The BSG's sorption capacities (mmol g−1), determined using the Langmuir model, ranged from 0.020 (Mn) to 0.041 (Pb), with measurements of uncertainty not exceeding 20%. It was determined that a relatively high concentration of calcium cations (7.5 mmol L−1) versus copper cation concentration (0.03 mmol L−1) in solution, restricted the sorption efficiency by approximately 80%. The optimum pH of the solution used to carry out the sorption was determined to be within the range of 4.5–5.5. It was found that the functional groups of the BSG lose their efficacy over consecutive sorption and desorption cycles due to being blocked, or due to their chemical decomposition. This indicated that the proper interpretation of the results requires a statistical assessment of the measurements of uncertainty and of the uncertainty of determination of the sorption parameters.