Developing a zero liquid discharge process for zeolitization of coal fly ash to synthetic NaP zeolite

• Coal fly ash zeolitized using a zero liquid discharge technique.
• Zeolitization of CFA is techno-economically feasible at larger scales.
• Elimination of liquid discharge will obviate the need to comply with environmental regulations.
• Zeolitic product can be used in eco-friendly technologies to immobilize different pollutants.

Successful conversion of coal fly ash (CFA) to synthetic NaP zeolite with zero liquid discharge is reported in this article. The process eliminates the need for large amounts of water and the need for a huge wastewater treatment unit. The need for water, as a make-up stream, is only to compensate water losses during sampling and drying. Savings associated with minimizing make-up water and eliminating wastewater treatment unit can be substantial. Water and sodium hydroxide consumption is reduced by 90% and 50%, respectively. Furthermore, quality of the NaP zeolite (CFA-ZP) obtained is comparable to conventional method. The zeolitized product shows high crystallinity and leach resistance toward heavy metal and trace element content of the product. Leaching tests revealed that the concentrations of most of trace elements in leachate of CFA-ZP were less than threshold limit for landfill leachate and wastewater effluent for discharging into river and surface water.