Fast-Pyrolysis Biochar from Invasive Eichhornia crassipes as a High-Capacity Adsorbent for Lead (II) Ions
Victor O. Genga
Department of Chemistry, Faculty of Science and Technology, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya.
Njagi B. Njomo
Department of Chemistry, Faculty of Science and Technology, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya.
Patrick K. Tum *
Department of Chemistry, Faculty of Science and Technology, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya.
Damaris N. Mbui
Department of Chemistry, Faculty of Science and Technology, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya.
Obed M. Nyabaro
Department of Chemistry, School of Pure and Applied Sciences, Kisii University, P.O. Box 408-40200 Kisii, Kenya.
*Author to whom correspondence should be addressed.
Abstract
This study evaluated biochar derived from the leaves and stems of Eichhornia crassipes for the adsorption of Pb(II) ions from aqueous solution. Dried biomass was thermally converted at temperatures between 300 and 700°C, and the resulting biochars were evaluated to identify the material providing the highest Pb(II) removal. Biochars produced at 300°C from leaves (BC300L) and stems (BC300S) were subsequently selected for batch adsorption experiments. The effects of contact time, adsorbent dosage, initial Pb(II) concentration, and solution pH were investigated. Maximum adsorption performance was observed at a contact time of 15 min and pH 5. The selected adsorbent dosage was 0.005 g, at which Pb(II) removal reached 95.24% for BC300L and 96.63% for BC300S under the reported experimental conditions. Adsorption capacity increased with increasing initial Pb(II) concentration. Equilibrium data were evaluated using Langmuir and Freundlich isotherm models. BC300S showed a stronger fit to the Langmuir model (R² = 0.9864), whereas BC300L showed a stronger fit to the Freundlich model (R² = 0.9595). The results indicate that biochar prepared from E. crassipes leaves and stems has potential for Pb(II) removal from aqueous systems. Further evaluation under continuous-flow, regeneration, and multi-component conditions is required to establish its practical applicability.
Keywords: Eichhornia crassipes, water hyacinth, fast pyrolysis, biochar; Pb(II), adsorption, heavy-metal removal, adsorption isotherms, Langmuir model, Freundlich model, wastewater remediation