Effective Removal of Ammonium from Aqueous Solution by Ball-Milled Biochar Modified with NaOH

The objective of this study was to investigate the feasibility of using modified biochars to enhance removal of ammonium from aqueous solution. The pristine, NaOH-modified, ball-milled, and NaOH-modified ball-milled biochars were prepared from wheat straw at 500 & DEG;C. The surface morphology and characteristics of biochar were obviously changed after modification. The NaOH-modification elevated the pH value and ash content of biochar, and the ball-milling treatment promoted the formation of oxygen-containing functional groups. The specific surface area of biochar (20.9 m(2)/g) increased to 51.4 m(2)/g and 145.6 m(2)/g after NaOH-modification and ball-milling treatment, respectively. The modified biochars showed considerable ammonium sorption capacity in a wide pH range (3-7), and the optimal pH of ammonium sorption was around 6. Both NaOH-modification and ball-milling treatment improved ammonium sorption on the biochars. Ammonium sorption of the biochars could be well fitted by the Langmuir and pseudo-second-order model, and the NaOH-modified ball-milled biochar showed the highest ammonium sorption capacity of 8.93 mg g(-1). The surface complexation with oxygen-containing functional groups and cation exchange were the dominant mechanisms of ammonium sorption on the biochars. These results indicate that NaOH-modified/ball-milled biochar has a good potential to be used for the ammonium removal from polluted water.