Development of barium@alginate adsorbents for sulfate removal in lithium refining

The demand for lithium has been steadily growing in recent years due to the boom of electric cars.High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte.Sulfate residuals originating from acid leaching of lithium ores must be limited to below 20 mg·L^(−1) during refining.There are methods to remove sulfate such as membrane processing and chemical precipitation using barium salts.However,membrane separation is unable to achieve the required purity while chemical precipitation often causes secondary contamination with barium and requires extra filtration processes that lead to increased processing costs.In this study,we developed a polymeric matrix entrapped with barium ions as a novel adsorbent to selectively adsorb sulfate in aqueous solutions.The adsorbent was prepared by dropwise injection method where alginate droplets were crosslinked with barium to form hydrogel microcapsules.In a typical scenario,the microcapsules had a diameter of 3 mm and contained 5 wt-%alginate.The microcapsules could successfully reduce sulfate concentration in a solution from 100 to 16 mg·L^(−1),exceeding the removal target.However,the microcapsules were mechanically unstable in the presence of an excess amount of sulfate.Hence,calcium ions were added as a secondary crosslinking agent to improve the integrity of the microcapsules.The two-step Ca/Ba@alginate microcapsules showed an exceptional adsorption performance,reducing the sulfate concentration to as low as 0.02 mg·L^(−1).Since the sulfate selective microcapsules can be easily removed from the aqueous system and do not result in secondary barium contamination,these Ca/Ba@alginate adsorbents will find applications in ultra-refining of lithium in industry.

Groundwater arsenic removal by coagulation using ferric(Ⅲ)sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic（As） in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric（III） sulfate（FS） and polyferric sulfate（PFS）performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca（ClO）_2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water（〈 10 μg/L） was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure（XANES） and As k-edge extended X-ray absorption fine structure（EXAFS） analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As（0.9 μg/L-0.487 mg/L）than the US EPA regulatory limit（5 mg/L）. Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.

Fluoride removal by Al,Ti,and Fe hydroxides and coexisting ion effect

Batch experiments were conducted to evaluate fluoride removal by Al,Fe,and Ti-based coagulants and adsorbents,as well as the effects of coexisting ions and formation of aluminum–fluoride complexes on fluoride removal by co-precipitation with alum（Al_2（SO_4）_3·18H_2O）.Aluminum sulfate was more efficient than the other coagulants for fluoride removal in the pH range between 6 and 8.Nano-crystalline TiO_2 was more effective for fluoride removal than Al and Fe hydroxides in a pH range of 3–5.Coexisting anions in water decreased the removal of fluoride in the order：phosphate（2.5 mg/L） 〉 arsenate（0.1 mg/L） 〉 bicarbonate（200 mg/L） 〉sulfate（100 mg/L） = nitrate（100 mg/L） 〉 silicate（10 mg/L） at a pH of 6.0.The effect of silicate became more significant at pH 〉 7.0.Calcium and magnesium improved the removal of fluoride.Zeta-potential measurements determined that the adsorption of fluoride shifted the PZC of Al（OH）_3 precipitates from 8.9 to 8.4,indicating the chemical adsorption of fluoride at the surface.The presence of fluoride in solution significantly increased the soluble aluminum concentration at pH 〈 6.5.A Visual MINTEQ modeling study indicated that the increased aluminum solubility was caused by the formation of AlF^（2＋）,AlF^（＋2）,and AlF_3complexes.The AlF_x complexes decreased the removal of fluoride during co-precipitation with aluminum sulfate.

Study on the Methods for Removing Sulfide Ion and Sulfate Radical from the Oilfield Sewage

Sulfide ion can reduce the viscosity of polymer solution. The higher the concentration of sulfide ion is, the greater the effect of viscosity on polymer is, and it directly affects oil recovery rate. Some methods for removing sulfide were studied by adding the oxidizing substances. Each method had certain effect on removing sulfide. The addition of hydrogenperoxide in the solution makes it faster to remove sulfide than flowing air in it, although the removal of sulfide is still not complete. This removal is quick when ozone takes part in, and it will spend much time with the increased volume of solution. The extent of removing sulfide was mainly related to the oxidability of re- moved substances. The stronger the oxidability of oxidizing substances was, the better the performance for sulfide removing was. In addition, part of sulfate radical in oilfield sewage could be removed by nanofiltration membrane. Removal efficiency of sulfate radical is about 50%. The probability may be avoided that sulfate radical was reduced into sulfide by the sulfate-reducing bacteria （SRB） in sewage. This method could radically reduce the presence of the reduction of sulfur in sewage, and it can reduce the corrosion of underground oil pipeline.