Zn-Al composite hydroxide by a co-precipitation method and its calcined products were prepared in different chemical composition. For the purpose of lowering calcination temperature and controlling particle morphology for ZnAl₂O₄ (spinel) synthesis, the obtained Zn-Al composite hydroxide was used as a precursor before a calcination operation.

Zn-Al-CO₃^2– LDH (Layered Double Hydroxide) is produced as a crystalline material in both chemical composition of spinel formation ([Zn²⁺]:[Al³⁺] = 1:2) and LDH formation ([Zn²⁺]:[Al³⁺] = 2:1). ZnAl₂O₄ is synthesized at lower calcination temperature of 700°C in the case of [Zn²⁺]:[Al³⁺] = 1:2. Zn-Al composite hydroxide with large plate-like particles is produced by applying a solvothermal treatment using ethylene glycol as a solvent to the Zn-Al composite hydroxide. When they are calcined, the composite oxide keeping the plate-like particle morphology of the precursor (Zn-Al LDH) is produced. It is clarified that ZnAl₂O₄ is synthesized at low temperature and the particle morphology is controlled by using Zn-Al LDH as a precursor.

This study aimed to facilitate efficient arsenic detoxification by inducing the microbial methylation of inorganic arsenic. Recombinant Escherichia coli strains K63 and KC42 were transformed to overexpress arsenic methyltransferase, and the methylation of inorganic arsenic was evaluated using the enzyme extracted from these strains. To ensure continuous reactions by maintaining enzymatic activity, the extracted enzyme was immobilized in microcapsules (MC) to catalyze the methylation of inorganic arsenic. The total yield of methylated organic arsenic compounds in strain K63 was 32.9% (after 2 h of incubation at pH 7.0 and 35°C), of which trimethyl arsenic compounds (TMAC) accounted for 8.3%. The total yield in strain KC42 was 35.9% (after 2 h of incubation at pH 6.5 and 35°C), of which TMAC accounted for 10.8%. When arsenic was methylated using MC prepared with the crude enzyme solution, the total yield of methylated organic arsenic compounds was 12.6% and 5.7% in strains K63 and KC42, respectively. The residual enzymatic activity was calculated to be 53.1% and 48.8% in strains K63 and KC42, respectively. Future studies should aim to increase the residual enzymatic activity, thus elevating the yield of organic arsenic compounds, by optimizing the conditions for enzyme immobilization in MCs.

Blast furnace (BF) slag is a byproduct of iron- and steel-making plants and is produced by the forced cooling of the 1500°C molten state. The ability to create value-added products from BF slag has become an important sustainability issue. In this study, we converted this slag into a hydrocalumite-like compound capable of removing pollutant ions from water through alkali fusion using the waste heat of the melting slag. The molten slag was transformed into a precursor with reactive phases by alkali fusion at 1500°C, after which the cooled melting slag was crushed and added to distilled water containing NaAlO₂ and stirred at room temperature to produce the hydrocalumite-containing product. The effects of the type of alkali salt, the Na₂CO₃-to-slag mixing ratio (Na₂CO₃/slag ratio), heating time, amount of added NaAlO₂, and the ability of the product to remove certain ions from aqueous solution were examined. Na₂CO₃ was used to alkali fuse slag at 1500°C, and the optimal conditions for the synthesis of hydrocalumite were found to include a Na₂CO₃/slag ratio of 2:1, a heating time of more than 10 min, and a 60 g/L concentration of NaAlO₂. The product was shown to remove more F^– and PO₄^3– than BF slag. These results suggest that a hydrocalumite-like adsorbent capable of removing pollutant ions from aqueous solution can be synthesized from BF slag through alkali fusion using waste slag-production heat.