Green, non-toxic and efficient adsorbent from hazardous ash waste for the recovery of valuable metals and heavy metal removal from waste streams

As compared to alkali-activated geopolymers with phosphoric acid which may be used in high concentrations resulting in disposal concerns, acid-based geopolymers may have superior properties. A novel green method of converting waste ash to a geopolymer for use in adsorption applications such as water treatment is presented here. We use methanesulfonic acid, a green chemical with high acid strength and biodegradability to form geopolymers from coal and wood fly ashes. The geopolymer is characterized for its physico-chemical properties and tested for heavy metal adsorption. The material specifically adsorbs iron and lead. The geopolymer is coupled to activated carbon forming a composite, which adsorbs silver (precious metal) and manganese (haz-ardous metal) significantly. The adsorption pattern complies with pseudo-second order kinetics and Langmuir isotherm. Toxicity studies show while activated carbon is highly toxic, the geopolymer and the carbon-geopolymer composite have relatively less toxicity concerns.

Automated summary

Compared to alkali-activated geopolymers, acid-based geopolymers offer superior properties and can avoid disposal concerns caused by high concentrations of phosphoric acid. In this study, a novel green method using methanesulfonic acid was developed to convert waste ash into a geopolymer for water treatment applications. The geopolymer showed excellent adsorption properties for heavy metals such as iron and lead. When combined with activated carbon, the geopolymer formed a composite that significantly adsorbed precious metal silver and hazardous metal manganese. The toxicity studies indicated that the geopolymer and carbon-geopolymer composite had lower toxicity concerns compared to activated carbon.