Synthesis of coal cinder balls and its application for COD_Cr and ammonia nitrogen removal from aqueous solution

Abstract

A new adsorbing material, coal cinder ball, was synthesized, characterized, and applied to remove chemical oxygen demand (COD_Cr) and ammonia nitrogen (-N) from water. Since coal cinders contain harmful metals, the optimum pretreatment method was determined by testing the harmful metal concentrations of cinder leachate solution. The results demonstrated the optimum concentration of HCl in modified coal cinders was 6 mol/L. Due to large surface areas of modified coal cinders, they exhibited a high adsorption affinity for COD_Cr and -N. The adsorption kinetics of COD_Cr and -N on coal cinder balls could be expressed by the pseudo-second-order model, which revealed that the adsorption process consisted of physical adsorption and chemical adsorption. The adsorption isotherms were fitted well with the Langmuir isotherm, which might be due to homogenous distribution of active sites on the microspheres’ surface. When the coal cinder balls were used to purify the micro-polluted river water, the removal of COD_Cr was much more than -N under different water volumes and packing lengths. When combined with zeolite at the ratio of 1:1, the removal rates of COD_Cr and -N increased significantly. This would overcome the shortcomings of zeolite single use and offer a wide application prospect in water treatment.

Keywords:

• Coal cinder ball
• Adsorption
• Zeolite
• Micro-polluted water
• COD_Cr
• -N

Acknowledgments

This work was supported by the 12th Five-Year Plan of National Science and Technology Support (No. 2015BAB07B02) and National Water Pollution Control and Management Technology Major Project of China (No. 2013ZX07202-007). The authors would like to thank the anonymous reviewers for their recommendations and comments.