This study investigates the impact of Mg(OH)2 on the in-situ formation of fibre-like aragonite and the mechanical properties of the cement mortar by accelerated carbonation. The results showed that the addition of Mg(OH)2 showed a weak effect on the compressive strength of carbonated samples, but it significantly improved the flexural strength of the carbonated samples. The flexural strength of carbonated sample increased with the addition of Mg(OH)2 content and the carbonated sample with 10% Mg(OH)2 showed approximately twice times than that of the hydrated sample at 28 d. The FTIR and XRD analysis also confirmed that aragonite became the dominate CaCO3 polymorph instead of calcite in carbonated sample with beyond 5% Mg(OH)2 content. The in-situ formed fiber/needle-like aragonite increased the total porosity of carbonated sample when adding Mg(OH)2 compared to the formed calcite in control sample due to the lower carbonation degree, while it refined the pore sizes of carbonated samples. Rhombohedral/cubic calcite and small amounts of long rod-like aragonite were present in the control sample. However, the dominant CaCO3 polymorph of aragonite with a length of 10–20 μm and an ammeter of 1–2 μm were generated in the samples incorporation of Mg(OH)2 and the length/diameter ratio of aragonite increased with the increased Mg(OH)2 dosages. This paper confirmed that reinforced cement composites can be prepared by controlled in-situ formation of fiber-like aragonite under carbonation curing and that an appreciable amount of CO2 can be sequestered. 

Increasing flexural strength of CO2 cured cement paste by CaCO3 polymorph control

Preparation of ceramsite from lead-zinc tailings and coal gangue: Physical properties and solidification of heavy metals

Syntheses, structures and properties of two keggin polyoxometalates [H5PCo(4,4'-bipy)Mo11O39][H3PMo12O40]·3.75(4,4'-bipy)·1.5H2O and [H3PMo12O40]·2(4,4'-bipy)·1.5H2O

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO₃ vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water. 

Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization.

A green heteropolyblue compound, (PPh4)4[PMo12O40] · 3DMF(1), has been synthesized from MoO3, H2O2 and H3PO4 in acetylacetone medium and crystallized from N,N-dimethylformamide. Compound 1 was characterized by analytical and spectroscopic methods, and X-ray structure analysis. The compound is a one-electron paramagnet and shows a featureless and cubic EPR spectrum with  = 1.95 in DMF glass. The complex shows a Mo(V)–Mo(IV) couple, which has been studied by cyclic voltammetric and coulometric methods. The compound acts as an efficient olefin epoxidation catalyst with H2O2 as oxidant and NaHCO3 as co-catalyst.

Synthesis and crystal structure of a mixed valence heteropoly green compound, (PPh4)4[PMo12O40], and its use as a catalyst in olefin epoxidation

Preparation of high-purity vaterite CaCO3 from lead-zinc tailings

The title compound H3[PMo12O40]· 3C2H6O was prepared and characterized by X-ray crystallography, its i.r. spectrum, cyclic voltammetry and e.s.r. spectra. The anion of the title compound is a Keggin-type heteropoly structure based upon a central PO4 tetrahedron surrounded by 12 MoO6 octahedra arranged in four groups of three edge-shared octahedra Mo3O13. Weak hydrogen bonds exist between the organic solvent molecules and the heteropoly anion. The catalytic activity of the title compound was determined by the synthesis of butyl acetate. The conversion of n-BuOH reached 93.3% and the yield of MeCO2Bu-n was 92.0% when the ratio of MeCO2H to n-BuOH, catalyst amount, reaction time, reaction temperature were 2:1, 0.24% of the reactants (50 mg), 2.0 h and 115 ∼ 120 °C, respectively.

Crystal structure and properties of H3[PMo12O40] · 3C2H6O

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Preparation of high-purity vaterite CaCO3 from lead-zinc tailings

Crystal structure and properties of H3[PMo12O40] · 3C2H6O