Desulfurization in high-sulfur bauxite with a novel thioether-containing hydroxamic acid: Flotation behavior and separation mechanism

Summary of sulfur hazards in high‑sulfur bauxite and desulfurization methods

With the gradual depletion of high-grade bauxite, the development of the alumina industry has been seriously constrained. High‑sulfur bauxite reserves are abundant and can be used as an effective supplement to bauxite resources. Therefore, the development of desulfurization and comprehensive utilization methods for high sulfur bauxite has been widely studied. Excessive sulfur content in bauxite and complex valence changes in the Bayer process have serious impacts on products and equipment. This paper will introduce pre-treatment desulfurization and post-treatment desulfurization methods such as roasting, flotation, electrochemical and biological methods. Roasting methods use oxidative roasting to convert sulfur to sulfur dioxide-containing flue gas; flotation methods enrich pyrite through flotation chemicals; biological methods use complex chemical reactions of microorganisms to remove sulfur; and electrolysis methods convert sulfur to sulfate through oxidants produced by electrolysis. Post-treatment methods add precipitants such as zinc oxide to treat small amounts of sulfur entering the Bayer process. The reaction mechanism and development of various desulfurization methods are summarized, and the problems of these desulfurization methods are analyzed. The aim is to combine their advantages to develop economical and environmentally friendly desulfurization methods, and propose suggestions for the future resource utilization of high‑sulfur bauxite.

Preparation of 6-Amino-N-hydroxyhexanamide-Modified Porous Chelating Resin for Adsorption of Heavy Metal Ions

The pollution of water bodies by heavy metal ions has recently become a global concern. In this experiment, a novel chelating resin, D851-6-AHHA, was synthesized by grafting 6-amino-N-hydroxyhexanamide (6-AHHA) onto the (-CH2N-(CH2COOH)2) group of the D851 resin, which contained a hydroxamic acid group, amide group, and some carboxyl groups. This resin was developed for the purpose of removing heavy metal ions, such as Cr(III) and Pb(II), from water. The findings from static adsorption experiments demonstrated the remarkable adsorption effectiveness of D851-6-AHHA resin towards Cr(III) and Pb(II). Specifically, the maximum adsorption capacities for Cr(III) and Pb(II) were determined to be 91.50 mg/g and 611.92 mg/g, respectively. Furthermore, the adsorption kinetics of heavy metal ions by D851-6-AHHA resin followed the quasi-second-order kinetic model, while the adsorption isotherms followed the Langmuir model. These findings suggest that the adsorption process was characterized by monolayer chemisorption. The adsorption mechanism of D851-6-AHHA resin was comprehensively investigated through SEM, XRD, FT-IR, and XPS analyses, revealing a high efficiency of D851-6-AHHA resin in adsorbing Cr(III) and Pb(II). Specifically, the (-C(=O)NHOH) group exhibited a notable affinity for Cr(III) and Pb(II), forming stable multi-elemental ring structures with them. Additionally, dynamic adsorption experiments conducted using fixed-bed setups further validated the effectiveness of D851-6-AHHA resin in removing heavy metal ions from aqueous solutions. In conclusion, the experimental findings underscored the efficacy of D851-6-AHHA resin as a highly efficient adsorbent for remediating water bodies contaminated by heavy metal ions.

High-efficiency adsorption removal for Cu(II) and Ni(II) using a novel acylamino dihydroxamic acid chelating resin

Cu/Ni-bearing wastewater contamination has recently been a challenge for the environmental protection worldwide. Herein, a novel poly(2-acrylamide-pentanedihydroxamic acid) (PAPDA) resin containing -CONHOH and -COOH groups was prepared and applied to effectively remove Cu²⁺ and Ni²⁺ from heavy metal wastewater. The batch adsorption experiments revealed that the maximum adsorption capacities of PAPDA resin for Cu²⁺ and Ni²⁺ were 436.08 and 195.05 mg·g^-1, respectively, which were 10.20 and 9.45 times higher than that of polyacrylic resin. Specifically, the adsorption kinetics and thermodynamics of PAPDA were respectively consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating that the adsorption is a single-layer chemisorption process. Besides, the adsorption mechanism was investigated by SEM, XRD, FT-IR, XPS, DFT calculations, suggesting that the PAPDA resin possessing abundant active sites could effectively adsorb the heavy metal ions. Noticeably, the -CONHOH groups represented the strong affinity towards Cu²⁺ and Ni²⁺ by forming stable five-membered rings. In addition, column experiments were conducted to study the practical adsorption process of PAPDA resin to heavy metal ions. Overall, the results proved that the novel PAPDA resin as a green and highly efficient adsorbent has a promising potential for the treatment of heavy metals-containing wastewater.

High-Efficiency Desulfurization of High-Sulfur Bauxite Calcined in a Conveyor Bed: Kinetics, Process, and Application

The reaction process, mechanism, and kinetics of the desulfurization of high-sulfur bauxite during calcination were investigated using thermal analysis–infrared analysis. A conveyor-bed calcination system was used to study the variations in the physical phase, desulfurization rate, and alumina dissipation rate of high-sulfur bauxite in the range of 500 °C–650 °C. The results show that sclerite monohydrate, kaolinite, rhodochrosite, pyrite, and dolomite mainly decompose during the calcination of high-sulfur bauxite, generating H2O(g), CO2, and SO2 as gaseous products. The decomposition of sclerite monohydrate and kaolinite and the dehydroxylation reactions of rhodochrosite and pyrite occur at <650 °C, with inseparable temperature overlap. High-sulfur bauxite desulfurization follows a three-dimensional spherical diffusion mechanism, with an activation energy of 181.16 kJ/mol, controlled by the diffusion rate of O2 or SO2 through the solid product layer. High-sulfur bauxite was calcined at 600 °C–650 °C for around 3.5 s in a conveyor bed, resulting in a negative divalent sulfur content of <0.03 wt.%, desulfurization rate of >0.98, and relative dissolution rate of alumina of >99%, satisfying the requirements of aluminum extraction via the Bayer method. The desulfurization rate predictions of the kinetic model were consistent with the experimental data.

Thermal treatment of Lanxess Lewatit® AF 5 resin used in the atmospheric chalcopyrite leaching process: Regeneration and sulfur recovery

Elemental sulfur is a key component in the acidic Albion chalcopyrite atmospheric leaching process and is a challenging issue in the residue. It has been proposed to use Lanxess Lewatit® AF 5 (AF 5) catalyst during the leaching of copper concentrates in the acidic Albion leach process, to eliminate the elemental sulfur from the leach residue. When using AF 5 during leaching, the copper and the iron recoveries were above 95% and 80%, respectively. The AF 5 collected 100% of the elemental sulfur and for a 1:1 ratio of AF 5 to concentrate, the loaded AF 5 gained 12.3 wt% sulfur after the first acidic Albion leach test and contained 24.3 wt% sulfur after two leaching tests. In this study, the optimum conditions for the removal of sulfur from the catalyst were investigated using a high temperature process in a laboratory tube furnace. The results indicated that the maximum desulfurization of 90.1% was achieved at 550 °C after 10 min. The regenerated AF 5 could be reused for several chalcopyrite leaching-AF 5 cycles. For the recycled AF 5, the sulfur absorption decreased by only 1.0% while the recoveries of copper and iron were not affected. The kinetic study showed that the activation energy for AF 5 desulfurization was 164.5 kJ/mol.

Highly efficient poly(6-acryloylamino-N-hydroxyhexanamide) resin for adsorption of heavy metal ions

Heavy metal wastewater pollution has become an ecological challenge worldwide. This study reports the development of a novel poly (6-acryloylamino-N-hydroxyhexanamide) (PAHHA) resin for effective adsorption of heavy metal ions, including Cu²⁺, Pb²⁺ and Ni²⁺. The chelating resin was synthesized by the grafting reaction between 6-amino-N-hydroxyhexanamide and polyacrylic resin, thus containing the hydroxamate and acylamino groups. The batch adsorption experiments revealed that the PAHHA resin exhibited an excellent adsorption performance for Cu²⁺, Pb²⁺ and Ni²⁺. The maximum adsorption capacities of Cu²⁺, Pb²⁺ and Ni²⁺ were determined to be 238.59, 232.48 and 115.77 mg·g^-1, respectively. Based on the adsorption kinetics, the pseudo-second-order kinetic model was noted to fit well for all metal ions. The metal ion concentration as a function of the equilibrium adsorption capacity fitted well with the Langmuir isotherm, thus indicating the single layer adsorption process. The adsorption mechanism was investigated by using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS) and adsorption isotherms. It was revealed that the PAHHA resin possessed multiple active sites, including -CONHOH, -CONH- and -COOH, which could strongly adsorb the metal ions. Specifically, the -CONHOH group displayed a high affinity by forming a stable five-membered ring with heavy metal ions. Overall, the developed resin exhibits advantages such as simple synthesis, inexpensive raw material and good recyclability, along with high adsorption ability, thus providing a new approach for efficiently treating wastewater contaminated with heavy metal ions.