Examining samarium sorption in biochars and carbon-rich materials for water remediation: batch vs. continuous-flow...

Samarium (Sm) sorption from aqueous solutions was evaluated in biochars (derived from castor meal (CM), eucalyptus forest residues (CE), sugarcane bagasse (SB) and green pericarp of coconut (PC)) and in other carbon-rich materials (coal fines (CF); two commercial activated charcoals (GAC, NGAC)) by applying batch and continuous-flow sorption experiments. Batch experiments revealed great K_d values, in the range of 10⁴-10⁵ L kg^-1, and high Sm sorption percentages (>97%, except for SB) in the range of environmental representative concentrations, using as-received materials, with no further treatments. Maximum sorption capacities were derived from sorption isotherms using the Langmuir model (from 1.2 to 37 mg g^-1). Continuous-flow sorption experiments permitted to obtain maximum sorption capacities by mass balance and by fitting the experimental breakthrough curves to Thomas and Yan models. CF exhibited the greatest maximum sorption capacity (40 mg g^-1) besting the commercial activated charcoals, while CM was established as the best biochar (7.2 mg g^-1), with similar results to NGAC (12 mg g^-1) but worse than GAC (36 mg g^-1). The contribution of cation exchange in Sm sorption was confirmed to be significant for most materials based on the analyses of cations leached during continuous-flow sorption experiments. Maximum sorption capacities derived from Langmuir fitting correlated well with maximum sorption capacities obtained from continuous-flow experiments. Both methods were confirmed to be suitable to determine the maximum Sm sorption capacity of the materials and then to propose the most suitable materials that can act as alternative to commercial activated charcoals.