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A new clean extraction technology for the decomposition of Bayan Obo mixed rare earth concentrate by NaOH roasting is proposed. The process mainly includes NaOH roasting to decompose rare earth concentrate and HCl leaching roasted ore. The effects of roasting temperature, roasting time, NaOH addition amount on the extraction of rare earth and factors such as HCl concentration, liquid-solid ratio, leaching temperature and leaching time on the dissolution kinetics of roasted ore were studied. The experimental results show that when the roasting temperature is 550 °C and the roasting time is 60 min, the mass ratio of NaOH:rare earth concentrate is 0.60:1, the concentration of HCl is 6.0 mol/L, the ratio of liquid to solid was (L/S) 6.0:1.0, and the leaching temperature 90 °C, leaching time 45 min, stirring speed 200 r/min, and the extraction of rare earth could reach 92.5%. The relevant experimental data show that the process of HCl leaching roasted ore conforms to the shrinking core model, but the control mechanism of the chemical reaction process is different when the leaching temperature is different. When the leaching temperature is between 40 and 70 °C, the chemical reaction process is controlled by the diffusion of the product through the residual layer of the inert material. The average surface activation energy of the rare earth element is Ea = 9.96 kJ/mol. When the leaching temperature is 75–90 °C, the chemical reaction process is controlled by the interface transfer across the product layer (product layer interface mass transfer) and diffusion. The average surface activation energy of rare earth elements is Ea = 41.65 kJ/mol. The results of this study have certain significance for the green extraction of mixed rare earth ore.

Usually, the extraction of rare earth by roasting with concentrated sulfuric acid is inevitably accompanied by the production of a large amount of SO3, SO2, HF, CO2 and other acidic waste gases, which accelerates the global greenhouse effect and ozone layer destruction. At the same time, a large amount of alkaline wastewater generated by NaOH decomposition of rare earth is difficult to be treated economically and reasonably, which makes it a major bottleneck restricting development. In this study, the clean technical route of Al(OH)3-NaOH mixed roasting rare earth concentrate is used. Compared with the traditional technology, such as concentrated sulfuric acid roasting, caustic soda roasting and sodium carbonate roasting, this route can achieve cost reduction and efficiency increase, and it has strong market competitiveness and green environmental protection advantages. The whole process makes full use of the strong complexing ability of Al and F, and realizes the selective conversion of F and Al resources and the efficient leaching of rare earth from various aspects and multiple angles. The whole process reduces F and CO2 pollution from the source and they are finally converted into aluminum industry production materials such as NaF, Na3AlF6 and Na2CO3, which provides a possibility for the green extraction of rare earths and the recycling of alkaline wastewater resource.

With the deepening understanding of the concept of sustainable development in the world, the roasting method of concentrated sulphuric acid with high pollution and energy consumption adopted by Bayan Obo rare earth ore has become a technical bottleneck and pollution source that seriously restricts the development of rare earth production enterprises. This paper proposes a new clean smelting technology for Bayan Obo rare earth ore, which mainly includes oxidative roasting, NaOH roasting, water washing and acid dissolution. The experimental results show that under the optimum experimental conditions, the washing rate of F and P can reach 63.21% and 17.24%, and the extraction of rare earth can reach 88%. Compared with the existing technology, the new smelting technology has greatly reduced the pollution of three wastes, which can not only realize the recovery of P and F, but also fundamentally alleviate the damage of P and F to the subsequent extraction process. Moreover, the amount of NaOH is less and Th resources are relatively concentrated. Both of them can be recovered economically and reasonably. The new smelting technology has the advantages of short process flow, simple operation and predictable environmental protection.

The effects of Se(IV) on the structure and function of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT) purified from the cytoplasm of Escherichia coli were studied. The coding region of human AS3MT complementary DNA was amplified from total RNA extracted from HepG2 cell by reverse transcription PCR. Soluble and active human AS3MT was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 degrees C. Spectra (UV-vis, circular dichroism, and fluorescence) were first used to probe the interaction of Se(IV) and recombinant human AS3MT and the structure-function relationship of the enzyme. The recombinant human AS3MT had a secondary structure of 29.0% alpha-helix, 23.9% beta-pleated sheet, 17.9% beta-turn, and 29.2% random coil. When Se(IV) was added, the content of the alpha-helix did not change, but that of the beta-pleated sheet increased remarkably in the conformation of recombinant human AS3MT. Se(IV) inhibited the enzymatic methylation of inorganic As(III) in a concentration-dependent manner. The IC(50) value for Se(IV) was 2.38 muM. Double-reciprocal (1/V vs. 1/[inorganic As(III)]) plots showed Se(IV) to be a noncompetitive inhibitor of the methylation of inorganic As(III) by recombinant human AS3MT with a K (i) value of 2.61 muM. We hypothesized that Se(IV) interacts with the sulfhydryl group of cysteine(s) in the structural residues rather than the cysteines of the active site (Cys156 and Cys206). When Se(IV) was combined with cysteine(s) in the structural residues, the conformation of recombinant human AS3MT changed and the enzymatic activity decreased. Considering the quenching of tryptophan fluorescence, Cys72 and/or Cys226 are deduced to be primary targets for Se(IV).

Hypoxia inducible factor 1α (HIF-1α) becomes an important regulation factor within the histiocyte when it is under the hypoxia condition. Recently, prolyl hydroxylases (PHDs) have been identified to inactivation HIF-lα by hydroxylation. In this study, polynitrogen compounds were screened as HIF-1α PHD3 inhibitors. The coding region of human PHD3 DNA was optimized by using synonymous codons according to the code bias of Escherichia coli . Soluble and active human PHD3 was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 °C. Mass spectrometry analysis of the resultant peptide product indicated a mass increase of 16 daltons, consistent with hydroxylation of the proline residue in the HIF-1α (556–574) peptide substrate. Polynitrogen compounds (1–4) inhibited the enzymatic hydroxylation of HIF-1α peptide in a concentration-dependent manner, and the apparent IC 50 values were 29.5, 16.0, 12.8 and 60.4 μM respectively. Double reciprocal (1/V versus 1/[HIF-1α peptide]) plots showed that these compounds are noncompetitive inhibitors of the hydroxylation by recombinant human PHD3 with K i values of 67.0, 25.3, 67.3, and 82.1 μM respectively. On the other hand, the metal complexes of these polynitrogen compounds (1–4) cannot inhibit the catalytical activity of PHD3. We hypothesized that the inhibitory mechanism of PHD3 activity by polynitrogen compounds is due to their binding to iron to form stable coordination complexes. Our results in this study indicated that polynitrogen compounds (1–4) could be potential inhibitors of PHD3 to regulate the transcriptional activity of HIF-1α.