Kinetics of Rare Earth Leaching from a Mangnese‐Removed Weathered Rare‐Earth Mud in Hydrochloric Acid Solutions

Corncob biocarriers with available carbon release for Chlamydopodium sp. microalgae towards enhanced nitrogen removal from low C/N rare earth element tailings (REEs) wastewater

Low nitrogen (N) removal efficiency limits the potential of microalgae technology for the treatment of high nitrogen and low carbon rare earth tailings (REEs) wastewater. In this study, waste corncob was utilized as a biocarrier immobilizing Chlamydopodium sp. microalgae to realize high-efficient treatment of the REEs wastewater. In only 2.5 d, corncob-immobilized microalgae allowed the residual concentrations of N lower than the emission standards, and ammonia nitrogen (NH4+-N) removal rate is 83.3 mg L-1·d-1, total inorganic nitrogen (TIN) removal rate is 86.7 mg L-1·d-1, which was 18.5 times that of the previously-reported microalgae (4.68 mg L-1·d-1). Compared with other microalgae immobilization carriers, corncob possesses the ability to release available carbon sources for microalgae. Composition analysis and sugar verification experiments showed that the main content of TOC released by corncob was monosaccharide, and in a certain range, the removal rate of N was positively correlated with the TOC concentration. The utilization of biomass wastes with dual functions as biological carriers has great potential to improve the performance of microalgae, and is conducive to the development of engineering applications.

Kinetics and mechanism of radium-isotopes dissolution in TENORM scale waste associated with petroleum production using certain organic carbon source: lactic acid solution-case study

The present study is conducted to explore the dissolution as inferred from the kinetic mechanism for radium-isotopes (²²⁸Ra, ²²⁶Ra, and ²²⁴Ra) in the TENORM scale waste deposited in oilfield pipes and equipment, Gulf of Suez, Egypt. The main efficiency factors for Ra²⁺-compound dissolution by lactic acid (LA) solution, e.g., reactive organic carbon (i.e., electron-donor source), have been investigated, and optimum chemical conditions have been determined. The obtained data were also employed to predict the leaching kinetics and mechanism of the Ra²⁺-isotopes removal by three shrinking core models (SCM, liquid film process-chemical controlled process-diffusion controlled process) and Arrhenius model. The maximum leaching percentage of Ra²⁺-isotopes reached to 55-60% at the optimal leaching conditions (0.3 M LA, 5 h, 25 °C, ϕ < 1 mm, S/L ratio 10/50 g mL^-1). The Ra-isotopes removal proceeds kinetically by diffusion-controlled process. Activation energy (E_a) of the leaching process was 10.51 kJ mol^-1. This value conforms that the leaching process for removal of Ra²⁺-isotopes in the TENORM scale waste by LA solution is controlled by a diffusion process. Values of thermodynamic parameters (∆G^o, ∆H^o, ∆S^o) were determined and indicate that dissolution of Ra²⁺-isotopes in the studied waste is non-spontaneous and temperature dependent. Moreover, the leaching mechanism may be attributed to the dissolution of soluble exchangeable and acidic species of Ra²⁺-species and/or these due conversions of insoluble Ra-sulfate to more soluble Ra-sulfide and/or Ra-hydrogen sulfide by LA solutions.