Soil Remediation, Waste Valorization and Biofuels from Cement Kiln Dust Landfills

Abstract

Abstract Bioenergy is viewed as a potential solution to anthropogenic greenhouse gas emissions. A sustainable deployment will depend on targeting marginal lands, particularly brownfield and degraded lands. In contrast, industrial remediation is often uneconomical or even desirable, especially if degraded lands passively return to a nature like state. Cement kiln dust landfills, containing saline solids, are such degraded lands that can be remediated biologically. Phytoremediation uses plants to transport a pollutant from contaminated soil into standing biomass. After harvest, it can be processed to separate salt, biofuel and process water. Work showed that salt recovery was preferential for large liquid to solid ratios with little effect for longer durations and higher temperatures. Elevated temperatures require additional energy while co-leaching more biomass, thus reducing total biomass to the kiln. Repeated soaking of smaller volumes of room temperature water also led to effective recovery. A multi stage design was investigated to reduce water consumption. The three stage counter current soaking method produced similar recovery while consuming 25% less water. The product is biomass with sufficient energy density for use as a solid fuel in the cement kiln at a carbon price below $20/t CO2. Long term remediation of cement kiln dust stockpiles is feasible on the century time scale while producing biofuel for the cement plant. Each square kilometer planted can substitute 5% of a cement kiln’s fuel while returning the waste to the kiln. This represents an early opportunity for combined remediation, waste valorization and bioenergy.