Electrodialytic Arsenic Removal from Bulk and Pre-treated Soil

Abstract

Arsenic (As) is a well-known highly toxic and carcinogenic element. A combination of electrodialytic remediation (EDR) after soil washing with flocculant addition targeting remediation of a soil polluted with As from wood preservation industry is the focus of this paper. The fine fraction (<\u20090.063\xa0mm) from the washed soil after dry sieving was also considered. The EDR experiments were carried out in a 2-compartment cell applying 0.01\xa0mA/cm2 during 14, 7 and 3\xa0days. The suspended soil slurry was placed in cathode compartment separated by anion exchange membrane (AEM) of the anolyte where the pH was kept at 10. The soil was highly polluted with As, and the EDR was able to remove between 50 and 80% corresponding to 400–478\xa0mg As/kg of soil. The major part of the As was removed within the first 3\xa0days (63%), and approx. 10% more of As was released doubling the time of the experiment: 72% in 7\xa0days and 80% in 14\xa0days. The pre-treated soil showed higher As initial concentration, but did not show a clear advantage in terms of removal rate as the original soil (not washed or sieved) showed 80% of As removal comparing with 61% and 50% for washed and fine fraction, respectively (although the absolute removed concentration was similar). The sequential extraction results confirmed that As was bound into more mobile fractions in original soil, and the higher removal was mainly due to its larger exchangeable and reducible fractions compared to the oxidizable and residual fraction in pre-treated soil.