High-Pressure Slurry Ablation (HPSA): An Emerging Liberation Technology
HPSA is a patented technology owned by Disa LLC, a startup minerals processing and environmental remediation company. Due to its unique application of energy, HPSA provides high shear conditions and has the potential to provide more efficient liberation of targeted minerals. Overall, the process entails a slurry stream containing the process material where the slurry is discharged from opposing nozzles at high velocities. The main principle of HPSA consists of high energy collisions between particles inside the high energy impact zone within the HPSA collision chamber, which causes the particles to dissociate and/or liberate into smaller particles increasing surface areas and improving the separation rate (a computational model of the collision zone is shown in Figure 1.). Exposed surfaces soften due to heat transfer from the slurry, and this thin, soft layer is easily liberated as a result of the low and mid-shear stresses inside the tank-pump-pipe design of the HPSA unit. This process is repeated until the entire particle is ablated. To achieve frequent and energetic collisions, slurry density must be high (>40% solids wt.). During the collisions, the particles undergo processes of distortion, deformation, and rebounding. During distortion and rebound, the sub phases of the particle distort differently because of their different physical properties which allows for more effective liberation. Liberation of the loosely bound subcomponents can then be easily separated via mechanical techniques such as gravity separation, size classification, or flotation. There are three main components to the HPSA system. The first is the feed loading and slurry transfer system. Component two is the pump nozzle assembly, or the collision chamber and the pumps that discharge through the nozzles. The final component is the solids classification and dewatering process. This part of the system is dependent on the application. For example, treated uranium tailings would be classified using a hydrocyclone and then dewatered using a decanting centrifuge.
Figure 1. Collision zone between two opposing nozzles.
Preliminary studies of HPSA have yielded very promising and there are several applications for HPSA integration. HPSA has the potential to significantly reduce specific energy requirements of conventional comminution circuits of ores with medium to low hardness which includes iron and nickel laterite ores, potash, phosphate, uranium and vanadium ores. Uranium mine tailings remediation has yielded significantly favorable results during testing campaigns. There are several hundred abandoned uranium mines throughout the Southwestern United States, and most still have large tailings piles that are dangerous to ecological and human life. Testing campaigns are conducted on a lab scale HPSA test skid. The pumps are mounted in such a way to minimize energy usage and wear within the system while maximizing the percent solids by weight. After the pump, a discharge ball valve is used to take samples after a specified residence time. Initial feed samples of the uranium tailings were classified using a wet sieve analysis using standard Tyler mesh sizes, and uranium concentration was measured in each mesh size fraction using an XRF and third-party analytical laboratories. Results found that most of the uranium was found in the coarser size fractions with 86% of the uranium residing in the +270 mesh sizes which accounted for 95% of the total sample mass. After four minutes of residence time in the HPSA process most of the uranium content was concentrated to the -270 mesh sizes. 93% of the uranium in the sample reported to the fines fraction which was only 19% of the total sample mass. Results indicate an 81% reduction in total waste since traditional approaches to uranium tailings clean up involve either transportation of all tailings to a licensed disposal site or the construction of an onsite repository. If 80% of the tailings are remediated to acceptable levels, then the cost of transportation and storage is reduced dramatically. Figures 2 and 3 are particle size distribution results with uranium concentration shown for pre and post HPSA results.
Figure 2. Pre HPSA results.
Figure 3. Post HPSA results.
Additional applications for HPSA have been examined thoroughly as well. Favorable results have been obtained for hydrocarbon contaminated soil remediation. Analytical results from DRO and GRO analysis concluded that the HPSA process reduces the total extractable hydrocarbons (TEH) by 80% in most circumstances. For example, one samples reduced THE levels from 18,800 ppm to 3,870 ppm. In the state of Wyoming, soil below 6,500 ppm can be buried on site with no further treatment or remediation. For iron mine tailings, HPSA proved to be a very effective comminution unit operation on top of liberation. Preprocess iron tailings had P80 values of 3,016 microns and after several minutes of processing, the P80 results were 1,319 microns. A dramatic decrease in particle sizes indicate future work with comminution focused studies could be successful. The iron ore project was one of Disa’s first pilot projects and resulted in the construction of a HPSA unit capable of processing 20 tons per hour as seen in Figure 4.
Figure 4. “Gen Alpha,” Disa’s first large scale unit.
HPSA has potential for various applications given the favorable results yielded from preliminary testing. Disa has established several strategic partnerships with organizations within the mining and mineral processing industry. Currently, Disa is partnered with a mineral processing engineering firm, Forte Dynamics, as well as with the University of British Columbia and Montana Tech.