2021-07-14_REVISION - M2012032 (4)

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FLSmidth USA,Inc. 7158 S FLSmidth Drive • Midvale • UT 84047-5559 • USA M ' O T H 1.0 Executive Summary Ouray contracted FLSmidth USA Inc. (FLS) to conduct thickening, rheology, and filtration testing on a Zinc Rougher Tailings stream from their Revenue mine site. The objective of the testing was to measure solid-liquid separation rates to predict sizing and operating parameters for a full-scale thickener and filter. FLS completed testing at their Solid-Liquid Separations Laboratory located in Midvale, Utah during April 2017. 1.1 Thickening The results of the thickening tests show that an anionic polyacrylamide flocculent with a very high molecular weight and medium charge produce the best overflow clarity and settling velocities. FLSmidth used SNF AN-926VHM for the testing campaign; however any flocculent meeting those criteria could work. Recommended flocculent dosage for the zinc rougher tailings stream is approximately 20 to 25 grams of flocculent per metric tonne of dry solids. Flux testing showed the optimum feedwell suspended solids concentration for flocculation is approximately 10 to 12 wt%. Dilution to the target feed solids concentrations can be achieved using the FLSmidth E-Duc® feedwell system and would not require additional water to the system. Thickening test results show that a thickener would accommodate a solids loading of 25-tpd/m2 or a minimum unit area of 0.04-m2/tpd. At this unit area, the thickener can produce an underflow solids concentration of approximately 60-wt% with approximately 30 minutes of solids retention time and a yield stress of approximately 25-Pa. The highest U/F solids that can be produced in the tailings thickener and still be managed with standard centrifugal pump is approximately 68-wt% with bed solids retention time of 3 hours. 1.2 Filter Press Testing FLSmidth engineers performed pressure filtration tests using a filter feed solids concentration of 60-wt%. This solids concentration was determined from the thickening test work. Client did not specify a target filter cake moisture. The testing offered sufficient data to determine full-scale filter sizing for the zinc rougher tailings stream. The pressure filtration conditions and results for two chamber thicknesses are presented in Table 1. Filtration rates will vary depending on Ouray's moisture requirement. In general, the 50-mm cake condition resulted in higher filtration rates at comparable cake moisture contents to the 32-mm cake, but the 32-mm cake resulted in the lowest ultimate cake moisture. Table 1: Summary of FLSmidth Filter Press Testing Results Zn Ro Tailings Chamber Condition Recessed Chamber Thickness mm 50 1 32 Feed Pressure bar 9.7 Cake Moistures wt% 14.9-20.0 13.3-20.6 Filtration Rates K /m2/hr 160-427 105-303 Page 1 1