Boron sorption by manganese oxide‐coated sand

Abstract

Manganese (Mn) in soils occurs mainly as hydrous oxides in the form of nodules, concretions or coatings on the surface of soil particles playing an important role in the retention of nutrients or heavy metals. Boron (B) is one of these elements found to be fixed by Mn‐oxides in a relatively available form. This research was conducted to study B sorption by Mn‐oxides prepared in the laboratory in relation to soil pH. Two Mn‐oxides were prepared as coatings on the surface of quartz sand, pyrolusite and birnessite. Boron sorption experiments carried out with uncoated sand (US), pyrolusite‐coated sand (PS), and birnessite‐coating sand (BS) showed that B sorption was increased in PS and BS in comparison to US. Total B sorption was greater on BS than PS and BS sorbed more unrecoverable B by dilute hydrochloric acid method. In US and PS, B sorption was linearly increased with pH. In BS, maximum B sorption occurred at pH 8.5. The operating mechanisms seems to be H bonds between boric acid and OH groups in pyrolusite and lingand exchange between borate and surface hydroxyls in birnessite.