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Analytical and experimental investigations into the coarse beneficiation of trona ore by sensor-based sortation and other physical separation methods
Bellusci, Nicholas
Bellusci, Nicholas
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2022
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2023-09-30
Abstract
Trona (Na2CO3•NaHCO3•2H2O) is a hydrated double carbonate salt mineral that is used to produce soda ash (Na2CO3), an important commodity used in glass manufacturing, water treatment, chemicals and detergents, paper and pulp production, and flue gas desulfurization. Approximately 30% of global soda ash production comes from trona mining and processing, and the world’s largest reserves of the mineral are found in Green River, WY.
Conventional processing of Green River trona ores utilize multiple unit operations, including comminution, size classification, calcination, dissolution, solid-liquid separation, evaporative crystallization, and dehydration. The variable presence of insoluble gangue species associated with trona in its natural ore contributes to highly demanding water-energy signatures associated with these process stages, to ultimately produce high purity soda ash. However, it has been speculated that the glass manufacturing industry may alternatively accept a lower quality product with a constituent insolubles content. As such, a means of beneficiating the ore at coarse size, thus rejecting the majority of the gangue prior to chemical processing by calcination, may allow for the production of such a product with improved water-energy efficiency.
This study investigates the means of applying physical separation techniques for coarse beneficiation of trona ore, to develop an overall water-energy efficient process that would produce a beneficiated-calcined product of insoluble content consistency for use as a soda ash substitute in glass manufacturing. Based on initial macroscopic visual differences noted between the ore and gangue at coarse size, sensor-based sortation was the primary beneficiation method evaluated.
An extensive characterization program was conducted on run-of-mine (ROM) trona ore samples to investigate the potential implications for beneficiation by sortation. The material was crushed to -3” and particle size analyses were performed to determine optimal size range and liberation for coarse beneficiation. Specimens of light, medium, and dark color from the material were manually selected, based on observations to the naked eye. Various analytical methods were used to prove a hypothesized correlation between the color range and composition of the specimens, for the purposes of distinguishing between ore and waste material. Supplemental analyses were also conducted to investigate potential byproduct recovery, thermal behavior of trona ore, and other coarse beneficiation methods including dry gravity separation and preferential degradation.
Imaging by x-ray transmission (XRT), laser-induced fluorescence (LIF), and color sensors was utilized for selected specimens, and a first inspection bench-scale sortation test was also completed on a bulk sample. Subsequent analyses on the imaged and sorted materials were performed respective to a conceptualized process flow diagram, to gain a preliminary assessment of the metallurgical performance for the beneficiation concept.
Results of the studies demonstrated that a -3” + 1” particle size range for the material is well suited for sortation in terms of liberation characteristics and separation efficiency. Significantly low concentrations of undesirable insoluble constituents, as low as <1% total mass, were found to be present in the light-colored specimens, whereas increasingly higher insoluble concentrations from medium to dark color were prevalent, thus proving the hypothesized correlation. Outcomes of the imaging and bench-scale sortation test found that LIF sensor-based sortation was the most promising in rejecting both the medium and dark-colored material bearing undesirable insoluble contents, and a beneficiated-calcined trona product of approximately 3.5% insoluble content was produced. A preliminary economic process assessment was conducted based on the projected performance of the sortation unit operation.
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