Removal of Al3+ and Mg2+ ions in wet-process phosphoric acid via the formation of aluminofluoride complexes.

With the decrease in the phosphate rock grade, the minor element ratios (MER) [(Fe2O3 wt% + Al2O3 wt% + MgO wt%)/P2O5 wt%] of wet-process phosphoric acid (WPA) exhibits a linear upward trend. This can lead to a huge challenge for the high-quality production of feed calcium phosphate salt (FCPS). In the present study, we proposed a novel and economical strategy to precipitate Al3+ and Mg2+ via the formation of aluminofluoride complexes (NaMgAlF6·H2O) with the anhydrous sodium sulfate (Na2SO4) and hydrofluoric acid (HF) as precipitation agents. Because of the low solubility of the complexes in WPA, the removal efficiencies of Al3+ and Mg2+ ions could reach 99.5% and 64.8%, respectively. The maximum mass loss of P2O5 was less than 0.5%. The precipitates could be separated and converted into the HF and Na2SO4 for reuse, thus further decreasing the cost of WPA purification.

Novel low-temperature H2S removal technology by developing yellow phosphorus and phosphate rock slurry as absorbent.

Recycling hazardous gas of H2S is one of the most important strategies to promote sustainable development. Herein, a novel method regarding purifying H2S is proposed by using yellow phosphorus and phosphate rock slurry as absorbent. The H2SO4, formed in situ by H2S conversion, can be devoted to decompose phosphate rock, and the spent absorption slurry was applied as raw material for the production of phosphorus chemical products. According to the characterization analysis, it was found that H2S was first oxidized to SO2 via O2 as well as O3 induced by P4. Subsequently, the generated SO2 dissolved rapidly in water to form H2SO4, and then reacted with the main component of phosphate rock, CaMg(CO3)2. Most notably, the active substances, such as, O3, SO4•- and OH•, produced in the reaction process, can oxidize H2S and HS- to these sulfur products. In addition, trace amounts of Fe3+ and Mn2+ that were dissolved from phosphate rock displayed a promotional effect on the formation of active substances. Consequently, as high as 85% of H2S removal efficiency can be obtained even under acidic condition and low temperature. The proposed H2S purification method offers a promising option for sulfur recovery and H2S pollution control.

An efficient and environmentally friendly process for the reduction of SO2 by using waste phosphate mine tailings as adsorbent.

The emission of SO2 and the disposal of waste phosphate mine tailings are generally regarded as two major environmental issues in phosphorus chemical activities. In this paper, an environmentally friendly and efficient route for removing SO2 from phosphorus chemical processes by using waste phosphate mine tailings as adsorbent was proposed. It was indicated that the desulfurization performance of the waste phosphate mine tailings was better than that of its raw ore. The characterization analysis illustrated that higher content of CaMg(CO3)2 was shown on the waste phosphate mine tailings, which played a dominant role in determining the better desulfurization activity. In contrast, the accumulation of PO43- and H+ ions resulted from the dissolution of Ca5(PO4)3F on the raw ore caused negative effect on SO2 removal. In the typical desulfurization system, the produced sulfuric acid from desulfurization process was used to decompose phosphate mine tailings, and these spent tailings can be subsequently applied as raw materials for the production of phosphorus products. As a result, the present approach can achieve the dual goal of reducing the cost of desulfurization process and recycling the waste tailings, which is of great environmental and economic significance.