Production and evaluation of granular activated carbons from rice husks for water treatment

Abstract

Rice husks (RH) is a great potential precursor for activated carbon (AC) for effective water treatment. However, inorder to improve activated carbon effectiveness and easy recovery, granular activated carbon (GAC) production was employed. The aim of this research was to obtain granular activated carbon from local under-utillised rice husk precursor (NERICA-10) and its efficiency for removal of heavy metal ions from wastewater was assessed. The rice husks were collected, cleaned, and alkaline pretreated using 2-4% w/v NaOH. The binders selected for the study were characterized and the most suitable binder with a high lignin percentage was selected. The pretreated rice husks were then granulated with a lignin binder. The pellet precursors were carbonized at a temperature (400 – 500 o C) heating rate (20 xi

o Cmin -1 ) and holding time (30-90 min). The carbonized char was further physically activated using steam at 850 o Cmin -1 o C, heating rate (10-30 ), and activation time (10 min). The response surface methodology (RSM) was employed to investigate the effect of the binder percentage (0 ≤ B ≤ 30 %) and particle size (0.3 ≤ S ≤ 1 mm) on pellet durability as well as carbon content. The effect of carbonization temperature (400 ≤ T ≤ 500 o C), heating rate (10 ≤ Y ≤ 30 o Cmin -1 ), and heating time (10 ≤ Z ≤ 30 min) on the char yield, fixed carbon, and ash content were also analyzed. The granular activated carbon was subjected to proximate analysis, Fourier transform infrared (FTIR) analysis and sorption studies. The sorption properties of GAC samples for the adsorption of Cu 2+ , Co 2+ , and Pb 2+ ions were analyzed. The ANOVA results revealed that binder percentage and carbonization temperature had asignificant influence on the granulation and carbonization process respectively. The optimized parameters for GAC production were found to be binder percentage (21.88%), particle size (0.65 mm), carbonization temperature (400 o C), heating rate (10 o Cmin -1 ), and hold time at peak temperature (30 min). Characterization of the produced GAC showed a low ash content (1.12%), high fixed carbon content (64.91%), and the presence of surface functional groups on FTIR analysis. Sorption studies showed that the heavy metal ion removal increased with an increase in the weight of the GAC dosage. The maximum efficiency of GAC heavy metal ions removal was found for copper (88.5% /4g of RH GAC), lead (90.5 % /8g), and cobalt (88.42%/8g). These results demonstrate that rice husk-derived granular activated carbon can remove heavy metal ions from wastewater and be an alternative low-cost precursor for granular-activated carbon production.