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DOE OSTI2020

Materials Data on Ca(AlGe)2 by Materials Project

CaAl2Ge2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca is bonded to six equivalent Ge atoms to form CaGe6 octahedra that share corners with twelve equivalent AlGe4 tetrahedra, edges with six equivalent CaGe6 octahedra, and edges with six equivalent AlGe4 tetrahedra. All Ca–Ge bond lengths are 3.06 Å. Al is bonded to four equivalent Ge atoms to form AlGe4 tetrahedra that share corners with six equivalent CaGe6 octahedra, corners with six equivalent AlGe4 tetrahedra, edges with three equivalent CaGe6 octahedra, and edges with three equivalent AlGe4 tetrahedra. The corner-sharing octahedra tilt angles range from 19–53°. There are three shorter (2.56 Å) and one longer (2.65 Å) Al–Ge bond lengths. Ge is bonded to three equivalent Ca and four equivalent Al atoms to form a mixture of distorted edge and corner-sharing GeCa3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ca3(AlGe)2 by Materials Project

Ca3(AlGe)2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Ca sites. In the first Ca site, Ca is bonded to eight equivalent Al and four equivalent Ge atoms to form a mixture of edge and face-sharing CaAl8Ge4 cuboctahedra. All Ca–Al bond lengths are 3.33 Å. All Ca–Ge bond lengths are 3.56 Å. In the second Ca site, Ca is bonded in a 7-coordinate geometry to two equivalent Al and five equivalent Ge atoms. Both Ca–Al bond lengths are 3.17 Å. There are one shorter (3.14 Å) and four longer (3.16 Å) Ca–Ge bond lengths. Al is bonded in a 2-coordinate geometry to six Ca, one Al, and two equivalent Ge atoms. The Al–Al bond length is 2.54 Å. Both Al–Ge bond lengths are 2.53 Å. Ge is bonded in a 7-coordinate geometry to seven Ca and two equivalent Al atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Engineering Calcium-Bearing Mineral/Hydrogel Composites for Effective Phosphate Recovery

Effectively recovering phosphate from wastewater streams and reutilizing it as a nutrient will critically support sustainability. Here, to capture aqueous phosphate, we developed novel mineral-hydrogel composites composed of calcium alginate, calcium phosphate (CaP), and calcium silicate (CSH) (CaP + CSH/Ca-Alg). The CaP + CSH/Ca-Alg composites were synthesized by dripping a sodium alginate (Na-Alg) solution with ionic precursors into a calcium chloride bath. To change the mineral seed’s properties, we varied the calcium bath concentrations and the ionic precursor (sodium dibasic phosphate (NaH 2 PO 4 ) and/or sodium silicate (Na 2 SiO 3 )) amounts and their ratios. The added CSH in the mineral-hydrogel composites resulted in the release of calcium and silicate ions in phosphate-rich solutions, increasing the saturation ratio with respect to calcium phosphate within the mineral-hydrogel composites. The CSH addition to the mineral-hydrogel composites doubled the phosphate removal rate while requiring lesser initial amounts of Ca and P materials for synthesis. Furthermore, by incorporating both CSH and CaP mineral seeds in composites, we achieved a final concentration of 0.25 mg-P/L from an initial 6.20 mg-P/L. Moreover, the mineral-hydrogel composites can remove phosphate even under CaP undersaturated conditions. This suggests their potential to be a widely applicable and environmentally-sustainable treatment and recovery method for nutrient-rich wastewater.

42 ENGINEERING↗