Preparation of biomimetic-bone materials and their application to the removal of heavy metals

Since heavy metals react with some components in bone, it can be surmized that these components would strongly fix heavy metals. Hydroxyapatite and a series of substituted-apatites that are likely to exist in bone were prepared under near-physiological conditions with the aim of developing materials that are capable of effectively removing low concentrations of heavy-metal ions at near-neutral conditions. The obtained apatites were characterized by inductively coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric and differential thermal analysis, and field-emission scanning electron microscopy. They were also tested for their ability to remove Pb, Cd, Hg, Cr, and As. The carbonate-substituted apatite exhibited very strong fixation of Pb²⁺, Cd²⁺, and Cr³⁺, and moderately strong fixation of Hg²⁺. Based on a heavy-metal-fixing mechanism, a bone-like composite, with chitosan as the saccharide portion and a polyaspartyl polymer as the protein portion, was synthesized via co-precipitation. The biomimetic composite was excellent at removing Pb²⁺, Cd²⁺, Hg²⁺, and Cr³⁺, with removal percentages as high as 99.8% and residual concentrations as low as 0.01 mg/L. However, the composite had little fixation of Cr₂O₇²⁻, CrO₄²⁻, or H₃AsO₃. When Cr(VI) was reduced to Cr(III), the percent removed increased greatly. © 2012 American Institute of Chemical Engineers AIChE J, 59: 229–240, 2013