Environmental behavior and engineering performance of self-developed silico-aluminophosphate geopolymer binder stabilized lead contaminated soil

A silico-aluminophosphate geopolymer (APG) binder was developed for Pb 2+ solidification/stabilization (S/S) treatment in our previous study, but the related performance of the APG stabilized Pb 2+ contaminated soil was not investigated. This study investigates the environmental behavior and engineering properties of APG binder stabilized Pb 2+ contaminated soil, and compares the S/S effect with cement and alkali-activated geopolymer cement by unconfined compressive strength, toxicity leaching, and pH-dependent tests, also explores the microscopic and mineral properties using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Results showed that the compressive strength of APG binder stabilized soil was higher than that of cement and alkali-activated geopolymer cement, the compressive strength increased with an increased APG binder content, increased first and then decreased with the Pb 2+ content increasing, reaching its maximum value when the Pb 2+ content was 2.0%. Under regular environment, the S/S effect of APG binder was basically consistent with that of alkali-activated geopolymer cement, in strong acid (pH = 2) and strong alkali (pH = 13) environment, the APG binder exhibited better S/S effect. The Pb 2+ leaching in soil stabilized with the APG binder prepared by solid powder activator was higher at 7, 14 days, but basically the same as that of using liquid activator at 28 days. The Pb 2+ leaching increased with electrical conductivity increasing, and there was a good correlation between Pb 2+ leaching and electrical conductivity. SEM and XRD analysis showed that different binders stabilized contaminated soil showed different morphology and mineral composition, Lead phosphate compound was formed in APG stabilized soil. In general, the APG binder has a good application prospect in treating contaminated soil under extremely acidic environment. • APG binder performed optimally for Pb 2+ contaminated soil solidification/stabilization. • APG binder stabilized contaminated soil has a better mechanical performance than cement and geoplymer. • APG binder has a stronger acid and alkali resistance than cement and alkali-activated geopolymer.