Evaluation of Two Aluminum Powders for Soil-Cement Applications

A detailed geo-environmental evaluation of two Al-rich waste powders from minerals purification and processing was conducted to evaluate their potential for specialty geotechnical applications such as soil cement. The fine powder contained very low totals and TCLP metals concentrations, while the coarse or agglomerated powder exceeded clean fill criteria for several metals. The fine powder was a highly crystalline material containing 73% corundum (α-Al₂O₃). SEM showed a homogeneous material, with well-formed corundum crystals from 30 to 100 μm in diameter. The solubility of Al in the pH range 11–12 was 20– 25 mg/L. The coarse powder was more inhomogeneous in, with only 43% corundum and Al also bound in gibbsite, Al metal and spinel; it also contained other compounds such as fluorite. The particle size of the coarse powder crystals was highly variable, with smaller (<10 μm) crystals aggregating to form larger particles. However, the Al solubility at pH 11– 12 was extremely high (3–4 g/L), but other metals were also solubilized (Cr, Se and Be). Interestingly, the superior Al solubility of the Al-2 powder did not result in higher unconfined compression strength (UCS) values in soil-cement mixtures. The Al-1 powder produced a 30% strength incresein the base cement at a 1% inclusion rate (relative dose) on a total pozzolan dose of 7% to the wet soil. This, coupled with its better environmental quality, led to additional product development research with the fine powder for specialty cement applications.