The reaction between alkali and coal powder may produce substances such as ferrous hydroxide, which is green.
The general process for hydrothermal synthesis of zeolite from fly ash is: fly ash → roasting (815°C) → NaOH hydrothermal treatment (90~100°C) → crystallization → let stand (10~16h) → add Na2SiO3→filtration→filtrate→washing→drying→zeolite products. Use NaOH or KOH as the activator to prepare an aqueous solution of appropriate concentration, mix a certain volume of alkali solution and a certain mass of fly ash evenly, age it for a period of time under certain temperature conditions, crystallize within an appropriate temperature range, and then filter the solution. Wash the solid with deionized water (until the pH value of the filtrate is about 10), and dry it at 100°C to obtain the zeolite product.