Jun Qu

Weathered crust elution-deposited rare earth ores are key strategic resources and the main source of medium and heavy rare earths. This paper summarizes the development of leaching technology of rare earth ores, compares the advantages and disadvantages of the three generations of leaching technology, and introduces the improved heap leaching technology and the new technology of the leaching–extraction integration and enhanced leaching, focusing on the leaching of weathered crust elution-deposited rare earth ores. In this paper, the development of the leaching agents is expounded, and the research status and the development trend of the composite ammonium salt leaching agent, impurity inhibition leaching agent, swelling inhibition leaching agent, and seepage-promotion leaching agent are also introduced. And this paper summarizes the leaching mechanism and the development direction of leaching agents. Moreover, the future key research direction of weathered crust elution-deposited rare earth ores is proposed, which is green, efficient, safe development and utilization.

In this study, a citric acid-soluble fertilizer of dittmarite (NH₄MgPO₄·H₂O) was synthesized by balling talc with NH₄H₂PO₄. The effects of ball milling speed and milling time on the dissolution rates of N, P and Mg in deionized water and 2% citric acid were explored. Characterization technologies such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG) and Scanning electron microscopy (SEM) were applied to test the prepared samples. In water, the prepared dittmarite was changed into struvite (NH₄MgPO₄·6H₂O) with almost no N, P or Mg release, while the dissolution rates of nutrient elements reached almost 100% in 2% citric acid. The proposed work presented a facile and environmentally friendly method to produce CASF with high agricultural and ecological value.

Mechanochemically prepared layered double hydroxide (M-LDH), which usually possesses high surface chemical activity and a substantial amount of surface defects, has presented outstanding application performance especially in the area of environmental protection. Recently published works on the mechanochemical synthesis of LDH were first introduced to provide a comprehensive summary on the preparation of the materials. Ensuing discussion provided an overview of recent research on the applications of M-LDH products as adsorbents and catalysts. The excellent adsorption performance and fast adsorption rate of the precursor of LDH produced by dry milling of raw materials was identified. The catalytic performances of M-LDH as catalysts, mainly photocatalysts, were then introduced. It is foreseeable that by rational utilization of mechanochemical processes and the unique chemical properties of M-LDH, increasing numbers of applications using M-LDH could be expected.