Rice husk ash-carbide lime as an alternative binder for waste foundry sand stabilization.

Rice husk ash (RHA) is an excellent pozzolana and associated with hydrated lime (HL), it becomes an alternative binder to Portland cement in soil stabilization. In the context of waste valorization, waste foundry sand (WFS) and carbide lime (CL) have been investigated in civil construction and environmental geotechnical applications. However, stabilizing WFS with alternative binders to Portland cement represents a large field of research to be explored. This study evaluated the stabilization of WFS with a binder based on RHA and CL, compared to the use of RHA-HL. An experimental design was carried out to evaluate the influence of different dry-specific weights (12.00, 12.75, and 13.50 kN/m3), RHA contents (10%, 20%, and 30%), and curing times (28, 60, and 90 days) under unconfined compressive strength (UCS). UCS results were submitted to statistical analysis and correlated to the porosity/binder content index (η/Biv). Healing capacity, mineralogy, microstructure, and leaching of metals from mixtures of interest were evaluated. The results showed that higher specific weights and higher percentages of RHA promoted better strength. The η/Biv0.28 index proved to be an adequate parameter to assess the UCS of WFS-RHA mixtures with different limes (CL and HL), lower porosity, and higher binder content leading to higher strengths. The mixture's mineralogy and microscopy showed the formation of cementing gels, corroborating the strength gains. WFS stabilized with both binders (RHA-CL and RHA-HL) presented satisfactory environmental performance, allowing the immobilization of metals in the waste compositions.

Leaching assessment of cemented bauxite tailings through wetting and drying cycles of durability test.

Disposal of mine tailings can cause negative environmental effects by releasing contaminants to surface and underground water. Alkali activation is a promising technique for immobilizing metals in stabilization/solidification of these wastes. This study evaluates the leaching behavior of cemented bauxite tailings (BT) submitted to weathering conditions. The alkali-activated binder was composed of sugar cane bagasse ash, carbide lime, and sodium hydroxide solution. Comparisons of the durability and leaching behavior of BT stabilized with alkali-activated binder and high initial strength Portland cement were performed. The durability results for alkali-activated were similar to the Portland cement, showing an average difference of 16%. Portland cement showed favorable results in the encapsulation of heavy metals like Cd and Hg, while the alkali-activated cement on Al, Cr, and Se. For Ba, Fe, Mn, and Zn immobilization, both types of cement presented an equal performance. The durability and leaching behavior of stabilized bauxite tailings is governed by the cement content and porosity of the blends, as well as their pH.