Boron removal from wastewater via coagulation sedimentation with ettringite: an experimental and mechanism study

摘要

Boron compounds that are largely being used in industrial processes may pose health risks to humans and animals due to unpredictable emissions to the environment. Nowadays, the boron (including its compounds) emission standard in Japan requires a more thorough removal of boron from all effluents than previously. Compared with other novel technologies, the coagulation process using ettringite as a purifying agent is known to be more economically effective, but the sophisticated water treatment method and mechanism have rarely been described. In this study, we wanted to clarify the boron removal mechanism by batch tests followed with measurement and data analyses on boron, calcium, aluminum, and sulfate in both the liquid and solid phases. Results indicate that increasing the pH from 10 to 13 enhances the removal of boron and also changes the amount of calcium, aluminum, and sulfate (sulfur and oxygen) in both phases. The mechanism suggested is that in aqueous solutions at high pH,OH-can drive a few sulfate and tetrahydroxy aluminate ions out of the boro-ettringite. Other measurements further detected the presence of two similar materials of boro-ettringite in precipitates that were formed at different pHs and observed to actually be mixtures.