Removal of selected toxic metal species from polluted water using cellulose extracted from sawdusts

Abstract

This study aimed at investigating the efficiency of raw sawdust from Eucalyptus saligna, Cupressus lusitanica, and Grevillea robusta species and their extracted cellulose compounds for the removal of lead and cadmium from polluted water. Cellulose compounds were extracted using n-hexane and ethanol as solvents, and chemically characterized by Fourier Transform Infra-Red (FTIR) spectroscopy technique. Both sawdust and extracted cellulosic compounds were assessed for their capability to remove lead and cadmium from polluted water by using batch and column flow methods. The analysis of the extracted cellulosic compounds by FTIR confirmed their nature with the presence of the absorption bands at 3450-3300 cm-1 characterizing alcoholic functions O-H stretching, 2910 cm-1 indicating C-H bond stretching for non-aromatic compounds, and this was completed by the appearance of absorption bands between 1450-1300 cm-1 for C-H scissing. Sharp band at 1100-1250 cm-1 indicating C-O stretch was also detected in the isolated cellulosic compounds. Raw sawdust of Eucalyptus saligna showed high adsorption removal (43.50% for lead and 33.40% for cadmium) compared to Cupressus lusitanica and Grevillea robusta sawdust while cellulose-based compound from Eucalyptus saligna also showed high adsorption removal (83.00% for lead and 72.30% for cadmium). In this study, adsorption parameters that include adsorbents dosage, contact time, pH, temperature and initial concentration of toxic metal were optimized and were found to be 1.75 g, 2 hours, pH 6, 25 °C and 10.0 mg/L, respectively. Batch and column flow adsorption experiments were used and the results showed that column flow mode highest efficiency removal for lead (94.00%) was achieved by using cellulose-based compounds from Eucalyptus saligna species (compared to that of 83.00%) for batch experiment mode at the same adsorbent. On the other hand, the highest efficiency cadmium removal was found to be 82.00% and 72.30% for column and batch experiment mode, respectively. The optimum parameters found were also applied to real sample collected from car garages and car washes at Gatsata, Kigali city, and the results showed a high removal efficiency for cellulose-based compounds extracted from Eucalyptus saligna species (94.00% for lead and 81.90% for cadmium) in column flow mode while it was 83.60% for lead and 72.41% for cadmium in batch experiment mode