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Using a cluster of pebbles to generate clumps is a common procedure to explore granular particles' micro- or macro-scale mechanical responses in DEM simulations. The struggle is to balance the number of pebbles and the shape accuracy of generated clumps compared to the original particles. A low-cost multi-image-based method is adopted in this paper to extract 3D triangular networks of original particles. A voxel-based clump generation method, namely V-CLUMP, is developed to generate clumps based on triangular networks. The operations, such as gradual discretization, surface cell optimization, and candidate pebble hollowing out, are proposed to improve the accuracy and efficiency of clump generation. The ideal of corner preserving is also adopted, and a novel image-based method to detect corners and ridges of particles or clumps is proposed in this paper. Clumps for four idealized geometrical shapes and five quintessential particles are generated using the V-CLUMP. The parameters, including the number of pebbles, volume, projection area, sphericity, roundness, and roughness, are used to evaluate the performance of the clump generation method proposed in this study. The result shows that the absolute value of the errors for most generated clumps with 30 to 120 pebbles in macro-scale descriptors, i.e., volume, projection area, and sphericity, are less than 6%. A better result of meso- and micro- descriptors, i.e., roundness and roughness, can be obtained by selecting optimum clump generation parameters. The code takes less than one second to a few minutes, within the acceptable limits. However, pebble hollowing out and corner detecting are still time-consuming, and more efficient algorithms are needed to improve the performance of the operations. [ABSTRACT FROM AUTHOR]

The filling barricade is one of the key components of roadway cemented backfill systems and this research focuses on critical factors influencing the performance of these systems, particularly the lateral stress characteristics and the stability of the filling barricade. In this paper, a theoretical model is presented and applied to obtain and calculate the lateral pressures exerted on the filling barricade and to understand the effects of the filling process. It is found that the yield stress of cemented backfill increases with curing time and this relationship can be described as an increasing power function. The lateral stresses exerted on the filling barricade increase over time during the filling period but decrease over time during the waiting period. Both the maximum lateral stress exerted on the filling barricade and the decreasing amplitude decrease as the number of filling rounds increases. In the calculation case, the maximum lateral stress declines from 0.161 MPa to 0.0148 MPa when the number of filling rounds increases from one to six. From these results, the filling process with three rounds is determined to be the optimal process scheme. In the first round, the lateral stress increases to 0.0369 MPa during the filling period and decreases to 0.0146 MPa during the waiting period; In the second round, the lateral stress increases to 0.0368 MPa then decreases to 0 MPa; in the third round, the lateral stress of the filling barricade stays at 0 MPa. [ABSTRACT FROM AUTHOR]

The possibility of using a centrifugal-gravity concentrator to reject Mg-bearing minerals and minimize metal losses in the flotation of base metals was evaluated. Sample characterization, batch scoping tests, pilot-scale tests, and regrind-flotation tests were conducted on a Ni flotation tailings stream. Batch tests revealed that the Mg grade decreased dramatically in the concentrate products. Pilot-scale testing of a continuous centrifugal concentrator (Knelson CVD6) on the flotation tailings revealed that a concentrate with a low mass yield, low Mg content, and high Ni upgrade ratio could be achieved. Under optimum conditions, a concentrate at 6.7% mass yield was obtained with 0.85% Ni grade at 12.9% Ni recovery and with a low Mg distribution (1.7%). Size partition curves demonstrated that the CVD also operated as a size classifier, enhancing the rejection of talc fines. Overall, the CVD was capable of rejecting Mg-bearing minerals. Moreover, an opportunity exists for the novel use of centrifugal-gravity concentration for scavenging flotation tailings and/or after comminution to minimize amount of Mg-bearing minerals reporting to flotation. [ABSTRACT FROM AUTHOR]

A study was conducted to compare laboratory kinetic test methods for predicting acid rock drainage rates of weathering. Five laboratory kinetic test protocols (standard humidity cells, non-aerated cells, tall cells, shaken cells and NP depletion columns) were evaluated by comparing sulfate release and NP depletion rates, and predicted time to acidity (defined as pH 6). Our tests indicate that the standard humidity cell creates an unnatural oxidizing environment due to its extreme wetting and drying cycles, and therefore produces erratic results. The non-aerated test cells likely create an oxidizing environment that more closely represents the natural conditions, producing more consistent results and therefore a better estimate of the sulfide oxidation rate. The practice of shaking cells to promote efficient rinsing of weathering products disturbs the oxidizing environment and may retard the oxidation rate. Accelerating NP depletion by the high addition of acidic water creates an unnatural leaching environment, producing results that are not consistent with those obtained from other testing protocols having more natural leaching environments. [ABSTRACT FROM AUTHOR]