Iván Salazar

The Maricunga Salar (Atacama Region, Chile; 3750–3800 m.a.s.l.) hosts Chile’s second-highest average lithium concentration in continental brines. This review integrates the scientific literature, technical resource-estimation reports and environmental information to provide a unified geological, hydrogeological and geochemical assessment of the basin and its resource evolution from 1982 to 2021. The brine averages 1122 mg/L Li (460–3375 mg/L), 12,847 mg/L Ca, 711 mg/L SO₄ and 311 g/L total dissolved solids. Although its Mg/Li ratio (6.53) is comparable to that of the Atacama Salar, its Ca/Li (11.45) and SO₄/Li (0.63) ratios distinguish Maricunga as the most Ca-rich and SO₄-depleted major Chilean salar brine. Comparison with other Andean brines reveals a systematic inverse Ca–SO₄ relationship, consistent with geochemical control by gypsum saturation. Maricunga occupies the Ca-rich endmember of this trend, which requires a Ca–Cl component; a deep hydrothermal origin is proposed as a testable hypothesis rather than an established result, because Na–Ca exchange within the basin fill cannot yet be excluded. Drainable porosity, determined from 561 undisturbed samples, ranges from 0.02 in the lacustrine core to 0.14 in marginal alluvial deposits. Importantly, the apparent increase in lithium resources between 1982 and 2021 primarily reflects progressive expansion of the investigated depth rather than increasing lithium grade, and the 2021 estimate refers to a block of only 11.25 km², less than 8% of the official salar surface. This synthesis therefore identifies hydrogeological architecture, rather than brine quality, as the principal development uncertainty, particularly regarding lateral continuity of the lacustrine unit and potential hydraulic connectivity with Laguna Santa Rosa and the Paipote drainage system. A recurring limitation is that most project-scale parameters derive from a single non-peer-reviewed technical report, so their reproducibility cannot be assessed independently from public data; resolving this, rather than acquiring further grade data, is the priority for advancing the basin towards development.

The economic value of rare earth elements (REE) is concentrated in Nd, Pr, Dy and Tb. The supply chain for these elements is dominated by a single country, China, which accounts for about 60% of mined production, over 90% of refinement, and nearly 95% of permanent magnet manufacturing. This shifts the critical question from geological availability to the capacity to convert resources into products. Chile hosts several domain types for REE: ion-adsorption regoliths, primary mineralization associated with skarn, iron oxide–apatite (IOA) and iron oxide copper–gold (IOCG) systems, pegmatites and placers, and an Exclusive Economic Zone with marine occurrences. The inventory is organized using a five-level evidence scale, compiled through structured searches of indexed databases and institutional repositories under explicit inclusion criteria. Only one record reaches level 1, Penco, with 27.5 Mt Measured and Indicated at 2292 ppm TREO and 62.9 kt contained TREO. Its grade is two to three times higher than that of ion-adsorption deposits abroad, but its tonnage is one to two orders of magnitude lower. Recoveries vary by element, from 19.53% for Nd to 43.23% for Dy, meaning that the REE oxide it contains does not equate to fully recoverable product. Nahuelbuta reaches 2000 ppm exchangeable, Cerro Carmen contributes 19.81 Mt containing 8203 t of rare earth materials and 1811 t of U, and El Buitre contains 6.6 Mt at 337 mg/kg. Reported concentrations span four orders of magnitude, but only two of the five measurement scales include an associated tonnage. Metallurgical recoverability follows the same pattern: saline desorption is mature and retains Th and U in the solid residue, acid leaching of copper residues reaches 64.5% at laboratory scale, the monazite–xenotime and apatite routes are proven but untested on Chilean material, and no domain has demonstrated separation capability. Opportunities lie in by-product recovery from iron and copper operations, modular development of the central-southern corridor, and domestic separation. Converting the available evidence into comparable figures would reshape the national hierarchy more than additional exploration.

Replacing clinker with mixtures of calcined clay and limestone is one of the most sustainable strategies for decarbonizing the cement industry. However, the kinetic patterns governing the grinding behavior of these materials are not yet fully understood. This study developed a kinetic model based on particle population balance to simulate this process. Experiments were conducted using a standard Bond ball mill, and the samples were characterized by X-ray diffraction. The results show that the grinding of calcined clay and its mixtures with limestone follows first-order kinetics. The proposed model simulates the process with a high degree of accuracy, with residual errors below 1.5% and a coefficient of determination exceeding 99%.

Determining nickel extraction during the roasting–reduction stage of the Caron process is an essential tool for controlling the metallurgical efficiency of the technology. This study evaluated the performance of a new semi-empirical kinetic model for predicting nickel extraction during the reduction of lateritic ores predominantly composed of iron oxides and oxyhydroxides in multiple-hearth furnaces. To achieve this, the lateritic ore was characterised by scanning electron microscopy (SEM) before and after the reduction process. The temperature in hearth six was varied between 495 and 780 °C by adjusting the post-combustion air supply. The proposed model demonstrated high predictive accuracy for nickel extraction, with absolute and residual errors below 1.70% and 1.15%, respectively. The findings emphasise the importance of controlling metallurgical efficiency through mathematical models that incorporate key technological variables and the kinetic behaviour of the process.

To date, the grinding behavior of saprolite and lateritic overburden mixtures remains poorly understood. The Bond Work Index (BWI) is the principal indicator used to determine the specific energy consumption during the grinding process. To establish the F₈₀ and P₈₀ values, granulometric distribution models—Rosin–Rammler (RR), Gates–Gaudin–Schuhmann (GGS), and the Swebrec function (SWEF)—were evaluated. The mineral phases of the feed samples were analyzed by X-ray powder diffraction. This study provides evidence that the RR function is the most suitable for simulating the particle size distribution of the feed material, with residual errors below 6.30% and a coefficient of determination (R²) exceeding 97%. After the grinding equilibrium cycle is reached, the SWEF model proves to be the most appropriate, exhibiting residual errors under 3.50% and R² values above 98%. BWI reveals that saprolite is the most difficult ore to grind, with specific energy consumption increasing from 16.38 kWh/t to 25.50 kWh/t as the proportion of saprolite in the mixture rises. This reflects a clear upward trend, as confirmed by a fitted model with an R² of 98.54%. In contrast, the grindability index (Gbp) decreases, indicating that the material becomes increasingly resistant to grinding as the saprolite content increases. This may be attributed to inherent material properties, such as hardness, or to physical phenomena related to fragmentation. The declining Gbp further suggests that greater energy input is required to achieve additional particle size reduction. Overall, the findings demonstrate that saprolite is inherently difficult to grind and behaves according to its own grinding characteristics, regardless of whether it is processed alone or in combination with lateritic overburden.

In the mining industry, key unit operations such as grinding, flotation, thickening, and tailings transport are negatively affected by the presence of clay minerals, which impart complex rheological behaviors to mineral suspensions by increasing their rheological properties. This deterioration arises from specific physicochemical characteristics of clay minerals such as fine particle size, anisotropic character, laminar morphology, and swelling capacity. This work reviews the effects of various rheology-modifying reagents on clay suspensions including kaolinite, illite, and montmorillonite. The reviewed reagents include inorganic salts, pH modifiers, polymers, surfactants, and nanoparticles. Their mechanisms of interaction with solid particles are analyzed, highlighting their influence on the degree of dispersion or aggregation. Furthermore, this review proposes research opportunities focused on the formulation of hybrid reagents, modified biopolymers, and the development of reagents effective under adverse conditions such as high salinity or elevated temperatures. This review provides a comprehensive basis for optimizing the use of rheological additives through more efficient and sustainable strategies for managing clay-rich suspensions in the mining industry.

The roasting/reduction process is one of the fundamental stages of Caron technology, ensuring the adequate transformation of lateritic ore, with post-combustion air feed being one of the main variables considered. In this study, new evidence is presented that justifies the negative effect that post-combustion air has on Ni extractions in H-6 of the furnace. With this objective, three air feed levels were evaluated, measuring the hearth temperature from 495 °C without post-combustion to 780 °C for the maximum post-combustion level analyzed. The evaluation was carried out in a conventional multi-hearth furnace at pilot scale using atomic absorption spectrometry, XRD, SEM, and particle size analysis as the main analytical techniques for the characterization of lateritic ore before and after the reduction process. Increasing the temperature of H-6 resulted in a significant decrease in Ni extractions by 1.68% for every 57 °C increase in hearth temperature, which was due to the resulting decrease in the reaction rate constant and the significant increase in the average particle size of the reduced ore. This research emphasizes the importance of controlling post-combustion air inflow as a technological alternative to optimize Ni extraction and reduce delays in the control of diffusive processes.

Due to the scarcity of high-grade minerals on the Earth’s surface and the ever-increasing demand for critical metals required in the production of clean energy, the search for alternative sources has become essential. Ferromanganese crusts, a mineral resource located in the depths of the ocean, contain high concentrations of valuable metals, particularly cobalt (Co) and manganese (Mn). A leaching process using sulfuric acid, with the addition of steel scrap, has been proposed for processing this resource. The study investigated the extraction of manganese (Mn) and cobalt (Co) under acidic conditions at 25 °C, employing a factorial experimental analysis. Statistical models were adjusted using response surface methodology to evaluate the effects of time and the ferromanganese crust/Fe(res) (iron residue) ratio as predictive variables. The results demonstrated that the extraction of Mn and Co could be effectively modeled through multiple regression, with strong goodness-of-fit indicators. Optimal extraction was achieved at extended durations (30 min) and lower ferromanganese crust/Fe(res) ratios (1/3) for the sampled values. Gradient analysis revealed that extraction efficiency was directly proportional to time and inversely proportional to the ferromanganese crust/Fe(res) ratio, except in the case of Co extraction at higher durations and lower ratio levels. Additionally, no precipitation of Mn or Co species was observed in the analyzed residues.

The Mine-to-Mill (M2M) approach aims to enhance efficiency and reduce costs in the mineral processing industry by optimizing the mining and processing stages. M2M integrates orebody characterization, blasting, and downstream processes, such as grinding and flotation, demonstrating that material fragmentation directly impacts downstream efficiency. This review studies the development and applications of fragmentation models in M2M integration and optimization, finding that their study is divided into three phases. In the first, the potential of M2M is investigated through simulation models that improve fragmentation in blasting to optimize grinding. The second focuses on the practical application of these models in mines, while the third phase integrates geometallurgical data into mine block models, enhancing production planning and selective ore extraction. The M2M integration has demonstrated significant improvements in plant performance, particularly in increasing grinding efficiency through optimized blast fragmentation. The literature also emphasizes the role of optimizing crushing and grinding conditions through models and circuit adjustments to enhance performance and reducing energy consumption. Geometallurgy plays a crucial role in plant optimization by identifying areas with better processing characteristics and adjusting operating parameters to maximize efficiency. Recent studies have shown how the implementation of integrated models can increase the profitability and sustainability of mining operations.

The letter represents the authors’ opinion on the positive impact that allowing open access to scientific publications has on doctoral programmes, the careers of young researchers and the overall quality of university education in Chile.