Aspect ratio-controlled preparation of α-CaSO4·0.5H2O from phosphogypsum in potassium tartrate aqueous solution

Synergistic preparation and application in PCU of α-calcium sulfate hemihydrate whiskers from phosphogypsum and electrolytic manganese residue

The α-calcium sulfate hemihydrate whiskers (α-CSHWs) were first prepared using phosphogypsum (PG) and electrolytic manganese residue (EMR) as raw materials for coating urea, demonstrating excellent controlled-release properties. The effects of different reaction conditions on α-CSHWs, achieved by optimizing the reaction time, the concentrations of NH4+, Mn2+, and other factors, were discussed. Results showed that when the EMR content was 25 wt%, the reaction temperature was 100 °C, and the reaction time was 3 h, α-CSHWs with a length-to-diameter ratio of 39 were obtained. Through experiments and density functional theory (DFT), the mechanism of α-CSHWs preparation was elucidated. The results show that the addition of EMR reduces the content of impurity ions PO43- and F- in PG while introducing NH4+ and Mn2+. Interestingly, both NH4+ and Mn2+ can reduce the nucleation time of α-CSHWs, while PO43-, Mn2+, and F- are more likely to adsorb on the (0 0 6) crystal plane of α-CSHWs, NH4+ readily adsorbs on the (4 0 0) crystal plane. The controlled-release performance of modified α-CSHWs incorporated into polyurethane-coated urea (PCU) was investigated, and it was found that the addition of Mα significantly prolonged the nutrient release period, with the period extending up to 116 days for coatings of 5wt% and above. This work not only enhances the efficiency of PG and EMR utilization but also serves as a reference for the straightforward synthesis and application of α-CSHWs.

Mussel-inspired dynamic facet-selective capping approach to highly uniform α-calcium sulfate hemihydrate crystals

We report herein a dynamic facet-selective capping (dFSC) strategy for α-calcium sulfate hemihydrate crystal growth from dihydrate gypsum in the presence of a catechol-derived PEI capping agent (DPA-PEI) with inspiration by the biomineralization process of mussel. The crystal shape is controllable and varies from long and pyramid-tipped prisms to thin hexagonal plate. The highly uniform truncated crystals have extremely high compression and bending strengths after hydration molding.

Leaching of phosphate ores with lower dissolution of metallic impurities: the dual role of sodium oleate†

In this work, we report the use of surfactants to improve the performance of phosphate ore leaching while reducing the concentration of metallic impurities in the leaching solution. Based on the zeta potential analysis, sodium oleate (SOL) is determined as a suitable surfactant because it can change interfacial properties and improve ionic diffusion. This is experimentally demonstrated by the high leaching performance. After that, the reaction conditions on the leaching performance are systematically investigated. Under the optimal experimental conditions (SOL concentration of 10 mg L⁻¹, sulfuric acid concentration of 1.72 mol L⁻¹, leaching temperature of 75 °C, and leaching time of 180 min), a high phosphorus leaching efficiency of 99.51% is achieved. Meanwhile, the leaching solution presents a lower content of metallic impurities. Further measurements performed on the leaching residues indicate that the additive SOL can promote the growth of platy crystals and facilitate PO leaching. Overall, this work demonstrates that the SOL-assisted leaching method allows for highly-efficient utilization of PO and high-purity phosphoric acid production.

A suitable surfactant, sodium oleate, is used to improve the phosphorus leaching efficiency while reducing the dissolution of metallic impurities, allowing for highly-efficient utilization of phosphate ores and high-purity phosphoric acid production.

α-calcium sulfate hemihydrate with a 3D hierarchical straw-sheaf morphology for use as a remove Pb2+ adsorbent

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate with a straw-sheaf morphology (3D α-HH straw-sheaves) are synthesized successfully in glycerin aqueous solution by a simple one-pot method, using as an efficient adsorbent for Pb²⁺ removal from water. The 3D straw-sheaf morphology, that closely depends on the glycerin/water volume ratio (V_Gly/V_H2O), can be accurately fabricated only when V_Gly/V_H2O is not lower than 3/1. 3D α-HH straw-sheaves are generated via multistep-splitting growth coupled with self-assembly. The obtained 3D α-HH straw-sheaves are further used as an adsorbent to remove Pb²⁺ from water, exhibiting excellent Pb²⁺ removal performance with an equilibrium adsorption capacity of 79.19 mg_Pbg_α-HH^-1 and removal efficiency of 98.98%, that both higher than those of plate- and columnar-like α-HH. Moreover, the experimental adsorption data for the 3D α-HH straw-sheaves is well fitted with pseudo-second-order kinetic model, and the adsorption isotherm is in good agreement with Langmuir model. The Pb²⁺ adsorption mechanism is thought to be a chemical adsorption process enforced by chemical bonding and ion exchange. This work demonstrates that 3D α-HH straw-sheaves are highly promising in removing Pb²⁺ from wastewater, thereby broadening the research field for the practical application of gypsum-based materials.

Self-Symmetrical 3D Hierarchical α-Calcium Sulfate Hemihydrate Twin-Flowers Composed of Microplates as a Renewable Material for Water Separation from Water-in-Oil Emulsion

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate twin-flowers with a self-symmetrical structure (3D α-HH HTFs) are synthesized successfully assisted by trisodium citrate (TSC). The morphology of α-HH is closely dependent on TSC, and with increasing TSC concentration from 0 to 15 mM, the morphology gradually evolves from a long column to rod, hexagonal plate, twin-flower-like, and eventually microgranule. 3D α-HH HTFs are formed via heterogeneous nucleation coupled with Ostwald ripening. The 3D α-HH HTFs are further used as an immobilized water material to separate water from a surfactant-stabilized water-in-oil emulsion, and exhibit excellent separation performance with a separation efficiency of 99.31 wt % and immobilization efficiency of 93.03 wt %. Impressively, the separated solid after water separation can be regenerated into 3D α-HH HTFs, which retain the high separation performance of the original 3D α-HH HTFs. This work demonstrates that 3D α-HH HTFs are highly promising in purifying oil with undesired water contamination.

An innovative method for manganese (Mn2+) and ammonia nitrogen (NH4+-N) stabilization/solidification in electrolytic manganese residue by basic burning raw material

High concentrations of manganese (Mn²⁺) and ammonia nitrogen (NH₄⁺-N) in electrolytic manganese residue (EMR) have seriously hindered the sustainable development of electrolytic manganese industry. In this study, an innovative basic burning raw material (BRM) was used to stabilize/solidify Mn²⁺ and NH₄⁺-N in EMR. The characteristics of EMR and BRM, stabilize mechanism of NH₄⁺-N and Mn²⁺, and leaching test were investigated. The concentrations of NH₄⁺-N and Mn²⁺ were 12.8 mg/L and 0.1 mg/L, respectively, when the solid liquid ratio was 1.5:1, and the mass ratio of EMR and BRM was 100:10, at the temperature of 20 °C reacting for 12 h Mn²⁺ was mostly solidified as bustamite ((Mn,Ca)Si₂O₆), groutite (MnOOH) and ramsdellite (MnO₂). NH₄⁺-N was mostly recycled by (NH₄)₂SO₄ and (NH₄)₃H(SO₄)₂. Leaching test results indicated that the concentrations of heavy metals were within the permitted level for the integrated wastewater discharge standard (GB8978-1996). Economic evaluation revealed that the cost of EMR treatment was $ 10.15/t by BRM. This study provided a new research idea for EMR harmless disposal.

Effect of Cu2+ on the nucleation kinetics and crystallization of rod-shaped CaSO4·2H2O in aqueous solution

In this study, a simple and efficient strategy is developed to synthesize rod-like CaSO₄·2H₂O (DH) crystals with tunable aspect ratio in aqueous solution using Cu²⁺ as modifier. The aspect ratio and length of the DH crystals are effectively reduced to 5.7 : 1 and about 35 μm in the presence of Cu²⁺, respectively. The interfacial tension value (γ) in the aqueous solution is improved significantly with the assistance of Cu²⁺, yet the nucleation rate (J) of the DH crystal is decreased sharply. The interfacial tension value (γ) in the aqueous solution is improved and the nucleation rate (J) of the DH crystal is drastically decreased due to the introduction of Cu²⁺, leading to the induction time of the DH crystallization being extended from 4 min to 25 min. The diversification of morphology for the DH crystals is incited by the changes of nucleation kinetics and Cu²⁺ incorporated into the crystal lattice, affecting the crystal growth habit, and finally controlling the growth of DH crystals in aqueous solution.

The induction time of DH crystals is extended by the introduction of Cu²⁺.