Conversion of Calcium Citrate to Citric Acid with Compressed CO2

Effective recovery of rare earth from (bio)leaching solution through precipitation of rare earth-citrate complex

Bioleaching is considered an alternative to traditional rare earth extraction technology. However, since rare earth elements exist as complexes in bioleaching lixivium, they cannot be directly precipitated by normal precipitants, which restricts their further development. This structurally stable complex is also a common challenge in various types of industrial wastewater treatment. In this work, a new method called a three-step precipitation process is first proposed to efficiently recover rare earth-citrate (RE-Cit) complexes from (bio)leaching lixivium. It consists of coordinate bond activation (carboxylation by pH adjustment), structure transformation (Ca²⁺ addition) and carbonate precipitation (soluble CO₃^2- addition). The optimization conditions are determined to adjust the lixivium pH to around 2.0, then add calcium carbonate until the n(Ca²⁺): n(Cit^3-) is more than 1.4:1 and lastly add sodium carbonate until n(CO₃^2-): n(RE³⁺) is more than 4:1. The results of precipitation experiments using imitated lixivium show that the rare earth yield is more than 96% and the impurity aluminum yield is less than 20%. Subsequently, pilot tests (1000 L) using real lixivium were successfully conducted. The precipitation mechanism is briefly discussed and proposed by thermogravimetric analysis, Fourier infrared spectroscopy, Raman spectroscopy and UV spectroscopy. This technology is promising in the industrial application of rare earth (bio)hydrometallurgy and wastewater treatment due to its advantages of high efficiency, low cost, environmental friendliness and simple operation.

Characterization and antivibrio activity of chitosan-citral Schiff base calcium complex for a calcium citrate sustained release antibacterial agent

Vibrio parahemolyticus is the "Number one killer" of seafood products. Anti-vibrio agents having low cost and high-safety are urgently needed to supplement the application needs. This work attempted to prepare CS-CT-CCa complex with citral (CT), chitosan (CS) and calcium citrate (CCa) as raw material by microwave-assisted high-pressure homogenization. Additionally the coordination structure and morphology of Bridge-CS-CT-Schiff base/OH-CCa were verified. The prepared CS-CT-CCa had a well-dispersed property (the size: 3.55~9.33 μm and the zeta potential: +38.7~+67.5 mV) and an excellent sustained released ability (sustained release up to 180 min). MIC, Glucose assay, MDA assay, biofilm formation inhibition assay, SEM, swimming and swarming motility assay demonstrated that CS-CT-CCa had strong (MIC of 128 μg/ml) and sustained (more than 12 h) inhibitory effects against V. parahaemolyticus. Meanwhile, CS-CT-CCa could increase the membrane permeability of V. parahaemolyticus and inhibit their biofilm-forming ability in a dose-dependent manner. It could be inferred that the antibacterial activities against V. parahaemolyticus caused inhibition of biofilm formation, swimming and swarming motilities. This study provided necessary data for the further design and development of chitosan antibacterial agents, food and feed additives.