Alkalinity neutralization and structure upgrade of bauxite residue waste via synergistic pyrolysis with biomass

Bauxite residues,a large volume solid waste,are in urgent need of effective disposal and management.Especially,strategies to alleviate the high alkalinity of bauxite residue remain a big challenge.Here,we developed a synergistic pyrolysis to neutralize the alkalinity of bauxite residue and upgrade the structure of biomass simultaneously.By cooperating the catalytic feature from bauxite residue,rice straw,a cellulose-enriched biomass,could prefer to produce acidic components under a hypothermal pyrolysis temperature(below 250℃)and partial oxygen-contained atmosphere as evidenced by the synchronous TGA-FTIR analysis.In return,these in-situ produced acidic components neutralized the bauxite residue profoundly(pH decreased from 11.5 to 7.2)to obtain a neutral product with long-term water leaching stability.Also,a higher pyrolysis temperature led to neutral biochar-based products with well-defined carbonization characteristics.Thus,the biomass-driven pyrolysis strategy provides a potential to dispose the alkalinity issue of bauxite residue and further opportunities for the sustainable reuse and continuing management of bauxite residue.

Accelerated alkalinity regulation and long-term dry-wet aging durability for bauxite residue remediated with biomass pyrolysis

Biomass fermentation provides a potential route toward the ecological disposal for the bauxite residue(BR)with high alkalinity issues.However,how to accelerate the remediation of the alkaline problem with a long-term durability is still a big challenge.Herein,we investigated the acceleration of the decomposition of straw toward organic acid species via a pyrolysis strategy as well as the pH stability during long-term dry-wet aging for the treated BR.The pH of pyrolytic BR at 300℃ is stabilized at around 8.90 after 70 days’dry-wet aging.During the aging,the main Ca-contained alkaline minerals of calcite and cancrinite are dissolved and the content of exchangeable Na+is reduced.This pyrolysis process can decompose straw quickly and produce more organic matters that are easily degraded to fulvic and humic acid as evidenced by 3D fluorescence spectrum analysis.Compared to the fermentation with straw under natural conditions,the alkalinity regulation of BR after pyrolysis is featured with shorter period and lower pH as well as long-term pH stability.Therefore,the synergistic pyrolysis of BR with straw provides an alternative method to address the alkaline issues,which is conducive to promoting the soil formation of BR.