Synthesis of inorganic polymers using fly ash and primary lead slag

► Inorganic polymers were made from 100% fly ash, 100% lead slag and mixtures of the two. ► Minerals dissolved and a new amorphous binding phase formed. ► The binding phase is rich in Si, Fe, Na and Pb and can reach >50wt.% in PbO. ► For 70:30 slag:fly ash inorganic polymers 19% water absorption 47MPa compressive strength. ► Leaching is pH dependant with Pb decreasing and Zn, As increasing in inorganic polymers. The present work reports on the synthesis and properties of inorganic polymers (“geopolymers”) made of 100% fly ash from lignite's combustion, 100% primary lead slag and mixtures of the two. In the inorganic polymers with both fly ash and lead slag the main crystalline phases detected are wüstite, magnetite, sodium zinc silicate, quartz, anorthite, and gehlenite; litharge partially dissolves. FTIR analysis in these samples revealed that the main peaks and bands of end members also exist, along with a new amorphous reaction product. In terms of microstructure, both fly ash and lead slag dissolve and contribute in the binding phase whereas the larger particles act as aggregates. For an increasing lead slag in the composition, the binding phase is changing in chemistry and reaches PbO values higher than 50wt.% for the 100% lead slag inorganic polymer. Regarding the properties of fly ash and lead slag inorganic polymers, compressive strength is higher than 35MPa in all cases and water absorption diminishes as the lead slag content increases. A comparison of leaching results before and after polymerisation reveals that pH is an important factor as Pb is immobilised in the binding phase, unlike Zn and As.