Chemical regeneration of spent empty fruit bunch biochar for sodium ion adsorption

Abstract

Biochar is a carbonaceous porous material produced by pyrolysis under oxygen-anoxic conditions. It has been widely adopted as an adsorbent to remove various pollutants from contaminated water due to its distinctive characteristics such as high porosity and surface-to-volume ratio, abundant functional groups, etc. One of the major problems in utilising biochar as an adsorbent is the recovery and sustainable management of the spent biochar. To determine the potential and reusability of biochar for wastewater treatment, the desorption and regeneration processes to reactivate the biochar should be studied and explored. This study aims to identify the desorption characteristics of sodium ions (Na+) on hydrothermal nitric acid pre-treated empty fruit bunch biochar (HNO3 EFB-BC). Different desorption eluents, i.e., tap water, deionised water, hydrochloric acid (HCl), sulphuric acid (H2SO4), sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). Among these eluents, HCl was chosen as the best desorbing agent for Na+, due to the highest desorption efficiency (66.23 %), at a concentration of 0.1 M. By using HCl, the exhausted HNO3 EFB-BC was regenerated up to six cycles. The Na+ desorption efficiency of HNO3 EFB-BC can be maintained as high as 69.03 % and 57.77 %, respectively, in the first two cycles. The efficiency of Na+ desorption remained as high as 18.85 %, after six successive adsorption and desorption experiments. The results have proven the potential of HNO3 EFB-BC as a cost-effective adsorbent for the sustainable remediation of saline solution. It also provided new insights to researchers on the desorption characteristics of HNO3 EFB-BC and display its potential to be regenerated from other cationic pollutants. Future desorption and regeneration studies should be performed using the actual saline soil or water with a mixture of pollutants to illustrate the effects of adsorbates on the performance of the regeneration process.