Converting fly ash into zeolite is

Converting fly ash into zeolite is an alternative way to reduce the waste landfills while also 31 producing high value-added products. However, hydrothermal synthesis of zeolite from fly 32 ash in alkaline media could also induce mobilization of toxic heavy metals, possibly causing 33 environmental contamination. Systematic research into this subject is rare in the open 34 literature and the mobility of heavy metals from fly ash derived zeolites is yet to be 35 understood. In the present contribution, we investigated the migration of heavy metals and 36 quantified their distribution from fly ash to product zeolites and waste water during the 37 synthesis of high-quality type A zeolites (471 m²/g surface area). High conversions of major 38 elements (98.2% aluminium and 96.5% silicon) were achieved, with zero secondary solid 39 waste. Metalloid elements including arsenic and selenium, and those with strong amphoteric 40 properties e.g. molybdenum were found highly mobile and mostly presented in the 41 wastewater. In comparison, less than 20% of the heavy metals with weak amphoteric nature 42 including copper, chromium and lead from the fly ash went to the wastewater; the rest along 43 with almost all cadmium, iron and nickel were fixed into the product zeolites. Despite the 44 existence of heavy metal elements in zeolites, there was no noticeable leaching under various 45 pH conditions, hence deemed safe for applications. Furthermore, the effective removal of 46 trace strontium and caesium cations from contaminated water using such zeolites was 47 demonstrated.