Metallurgical and Materials Data

Hydrogen in Treatment of Bauxite Residues

2025-03-04T11:02:46+00:00

This study explores pyrometallurgical and hydrometallurgical methods for decarbonizing and recovering valuable metals from bauxite residue, with direct hydrogen reduction in a rotary kiln without smelting and dissolution of solid residues under high pressure in an autoclave. The goal is to offer decarbonizing techniques for the removal of iron from bauxite residue, a by-product of the Bayer process, which cannot be disposed of in an environmentally sustainable manner. In contrast to traditional carbon-based reductive melting, which generated significant CO₂ emissions, hydrogen is now being investigated as a cleaner alternative. Through hydrogen reduction in rotary kiln, approximately 99.9% of iron is recovered as iron, which can be separated using magnetic separation from the solid residue containing other valuable metals. We concluded that hydrogen can reduce iron oxide from bauxite residues to metallic iron in contrast to very stable oxides such as titanium oxide, silica and aluminum oxide. Leaching of titanium, iron and aluminum with sulfuric acid has high efficiency under high pressure in an autoclave.

A Review of Laboratory Methods for Metal Recovery from Red Mud: Extraction Strategies and Technological Insights

2025-03-11T09:39:48+00:00

Red mud, a solid waste byproduct from alumina production via the Bayer process, represents a potentially valuable secondary resource. The global scientific community is increasingly focused on developing environmentally friendly and economically viable technologies for red mud recycling. This review summarizes findings from 162 scientific publications, with emphasis on studies related to the extraction of valuable elements such as iron (Fe), aluminum (Al), sodium (Na), and titanium (Ti). Reported concentrations of key oxides in red mud vary significantly depending on bauxite composition and processing route, with Fe₂O₃ ranging from 7–70 wt.%, Al₂O₃ from 2–33 wt.%, TiO₂ from 2.5–22 wt.%, and Na₂O up to 12.5 wt.%. Maximum extraction efficiencies achieved under laboratory conditions reached 97.5% for iron, 89.7% for aluminum, 96.4% for sodium, and 97% for titanium.

The analysis highlights the predominance of laboratory-scale studies, with limited transition to industrial applications. Integrated processing schemes—such as reduction smelting, magnetic separation, and leaching with mineral (HCl, H₂SO₄, HNO₃) and organic (H₂C₂O₄) acids—are identified as particularly promising. Emerging methods involving microwave, ultrasonic, and plasma-assisted treatments are also discussed. However, economic feasibility remains a major uncertainty. This review proposes a structured overview of current extraction technologies and outlines criteria for processes that balance environmental, energy, and cost considerations. Additionally, the article presents laboratory results on combined extraction schemes and explores the use of red mud in mold separation coatings.

Sodium Cyanide Generation by Coal Gasification

2025-03-03T13:08:15+00:00

This study investigates the technological feasibility of producing sodium cyanide through coal gasification, focusing on the influence of key process parameters—temperature, reaction duration, and coal type—on the concentration of sodium cyanide in the resulting solutions. Experiments were conducted on a laboratory-scale setup featuring a tubular corundum furnace. Lignite and charcoal, pre-crushed to increase specific surface area, were used as carbon sources. Sodium cyanide was obtained by capturing hydrocyanic acid (a syngas component) through sorption in a sodium carbonate solution. Absorption was enhanced by using a NaOH solution (pH = 10) maintained in an ice bath. Sodium cyanide concentration in the solution was determined using a titrimetric method, while thermodynamic simulations were performed using HSC Chemistry 5.1.

Gasification of charcoal within the 600–800 °C range yielded sodium cyanide concentrations between 0.03–0.08 wt%. However, raising the temperature to 900 °C under identical experimental conditions resulted in a fourfold decrease in NaCN concentration. A regression equation was derived to describe the dependence of NaCN concentration on gasification temperature and process duration. The findings confirm that sodium cyanide concentrations achieved under laboratory conditions are comparable to those required for gold cyanidation in gold recovery plants. Implementing on-site sodium cyanide generation at mining facilities could significantly reduce production costs by eliminating the need for external procurement, transportation, and storage of reagents.

Geopolymerization in Fly Ash and Flotation Tailings: Thermodynamic Modeling

2025-03-28T09:38:29+00:00

This study presents a thermodynamic modeling approach to the geopolymerization of fly ash (FA) and flotation tailings (FT), aiming to predict the physicochemical composition of the resulting geopolymers based on the input materials, alkali activators, and water. Simulations were performed using the GEM-Selektor software (Gibbs Energy Minimization) for four different FA-FT ratios (100%, 80%, 65%, and 50% FA). The model's predictions were validated against experimental data by comparing the geopolymerization products to structural and mechanical properties characterized via Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) and Unconfined Compressive Strength (UCS) measurements after 28 days of curing.

The results demonstrated that increasing fly ash content led to greater formation of C-A-S-H phases. The model also underscored distinguishing between C-A-S-H and N-A-S-H proportions in evaluating material stability. Both experimental findings and literature emphasize maintaining optimal molar ratios of Ca/Si, Si/Al, and Na/Al to ensure geopolymer integrity. This model provides a valuable predictive tool for optimizing geopolymer formulations, reducing the need for extensive experimental trials.

Development of Clay-Based Porous Filters Using Boric Acid for Industrial Liquid Separation

2025-03-13T09:28:14+00:00

Sedimentary materials such as clay are attractive for producing porous ceramics due to their low cost and natural abundance. Porous ceramics offer a unique combination of desirable properties—particularly high porosity and excellent thermal and chemical stability—which are essential for various industrial and environmental applications, including filtration, insulation, and absorption. In this study, purified clay was combined with boric acid, selected for its affordability and environmentally friendly characteristics, to develop porous clay-based filters. The influence of boric acid content (0.5 wt.% and 2 wt.%) under different synthesis conditions was investigated. The results showed that optimal filter hardness and uniform pore distribution were achieved under specific combinations, demonstrating the potential of boric acid-assisted clay formulations in the production of efficient, sustainable filter materials.