Leaching calcium from phosphogypsum desulfurization slag by using ammonium chloride solution: Thermodynamics and kinetics study

Advances in Phosphogypsum Calcination and Decomposition Processes in Circulating Fluidized Beds

Phosphogypsum (PG) is an industrial hazardous waste product discharged during wet-process phosphoric acid production. Once crystallized, the byproduct PG is filtered and separated from the liquid-phase product and sluiced to the disposal area near the production site for storage, seriously threatening the harmonious symbiosis between humans and nature. Therefore, devising effective solid waste management and cleaner production programs to contain and eliminate PG is of interest to researchers. In this study, the utilization status of PG is comprehensively reviewed, and a feasibility pathway for resourceful recovery of PG is proposed. The key challenges and countermeasures for the high-temperature calcination and decomposition of PG are analyzed and discussed. The visualization analysis based on bibliometrics reveals that the maximum recovery of abundant calcium (as CaO) and sulfur (as SO2) in PG and their utilization for the copreparation of calcium-based materials and sulfuric acid are the most suitable solutions for the large-scale application of PG. Five challenges that restrict the commercial promotion of PG calcination and decomposition processes are perfecting the calcium-sulfur conversion mechanism, establishing a process strengthening strategy, developing value-added technology routes, mastering unit scale-up regularity, and conducting sustainable performance assessment. Industrial applications are expected within 10-15 years.

Recycling lead from copper plant residue (CPR) using brine leaching - Precipitation - Calcination process

Copper plant residue (CPR) is a hazardous industrial by-product possessing both high toxicity and valuable metal content, necessitating its high value-added utilization. Traditional practices in smelters involve stockpiling and landfilling of CPR, leading to substantial land occupation and water contamination. This study focused on the preparation of PbO and Pb3O4 using the HCl-NaCl leaching-conversion-thermal decomposition process, employing CPR as the primary raw material. The effect of various leaching process conditions on the metal leaching rate was explored. A maximum lead leaching rate of 87.65% was achieved under optimal conditions including leaching temperature, liquid-solid ratio, leaching time, HCl molar concentration, NaCl mass concentration, and particle size. The lead content in the leachate was 15.85 g/L. Experimental data indicated that ash diffusion control served as the rate-limiting step in the HCl-NaCl leaching process. The apparent activation energy was determined to be 18.374 kJ mol-1, with a reaction order of 0.8986 concerning the HCl concentration and an L/S ratio of 0.8124. Additionally, response surface methodology enabled the determination of technological parameters for refining PbCl2 into PbCO3 precursors, yielding a conversion rate exceeding 96.50%. Moreover, the technical indicators of PbO and Pb3O4 obtained through low-temperature thermal decomposition of PbCO3 were investigated. The fabricated PbO and Pb3O4 exhibited purities of 99.65% and 99.26%, respectively, effectively transforming CPR from hazardous waste residue into valuable products. The process ensures the efficient recovery of lead to its maximum extent and promotes residue recycling.

A new basic burning raw material for simultaneous stabilization/solidification of PO43--P and F- in phosphogypsum

Phosphogypsum (PG) contains a lot of soluble phosphate (PO₄^3--P) and fluorine ion (F^-), which seriously has hindered the sustainable development of the phosphorous chemical industry. In this study, a new burning raw material (BRM) as an intermediate product in the cement production process was used for PO₄^3--P and F^- stabilize in PG. The stabilizing mechanism of PO₄^3--P and F^- were investigated by Fourier Transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM), X-ray fluorescence (XRF) and X-ray spectroscopy system (XPS). The effect of PG and BRM weight ratio, solid-to-liquid ratio, reaction time, and reaction temperature on the concentrations of PO₄^3--P and F^- were studied. The results showed that the concentration of F^- in the PG leaching solution was 8.65 mg/L and the stabilizing efficiency of PO₄^3--P was 99.78%, as well as the pH of the PG leaching solution was 8.12 when the weight ratio of PG and BRM was 100:2, and the solid to liquid ratio was 4:1, reacting for 24 h at the temperature of 30 ℃. PO₄^3--P and F^- were mostly solidified as Ca₅(PO₄)₃F, CaPO₃(OH), Ca₅(PO₄)₃(OH), Ca₂P₂O₇·2H₂O, CaSO₄PO₃(OH)·4H₂O, CaF₂, and CaFPO₃·2H₂O. Leaching test results indicated that the concentrations of PO₄^3--P, F^- and heavy metals were less than the integrated wastewater discharge standard (GB8978-1996). This study provides a new harmless treatment method for PG.

New Insights into the Mechanism of Enhanced Performance of Li[Ni0.8Co0.1Mn0.1]O2 with a Polyacrylic Acid-Modified Binder

A binder is an important component in lithium-ion batteries and plays a significant role in maintaining the properties of active substances. Most studies in the field of binders have only focussed on physical properties such as bonding performance. Here, a polyacrylic acid-modified binder was designed and adapted to Li[Ni_0.8Co_0.1Mn_0.1]O₂, which enhanced the electrochemical stability of Li[Ni_0.8Co_0.1Mn_0.1]O₂ from 30.2 to 66.6% (300 cycles at 1 C). We for the first time discovered that this was caused by a chemical reaction between polyacrylic acid and the residual lithium on the surface during the cycling, which formed a lithium propionic acid coating layer and maintained the stability of the layered structure.