THE HW EMS~(TM) METHOD AND REFRACTORY AU ORES (Engineered Membrane Separation)

摘要

The solutions used in the heap biooxidative treatment of sulfidic refractory Au ores and concentrates generally load free mineral acid and metals and, in time, become bacteria activity inhibiting due to increased acid and/or metals concentrations. The metals-acid loaded, bacteria action inhibiting, solution must then be: (a) processed, prior to re-use, to reduce its metals and/or free acid mineral acid components to bacteria activity compatible levels; or (b) neutralized prior to discharge. The most common solution processing method to adjust acid-metals contents is liming to effect the precipitation of dissolved metals and neutralization of acid sufficient for solution discharge or re-use. The lime treated solution is high in suspended, colloidal precipitates and requires clarification before reuse. Most often the "bleedstream" of biooxidation solution that is lime treated is discharged and requisite volumes of fresh water added to the process inventory. Depending on the level of bacterial action in a heap and the acid consumption characteristics of the ore/concentrate being biooxidized, the bleedstream taken from the circulating, irrigation on-off, solution, can be large (e.g., 10 percent -20 percent and sometimes as much as 50 percent of the daily solution flow requires treatment-discharge). The lime charge for bleedstream treatment is commensurately large and represents a major operating cost of the biooxidation process. The patented HW Process Technologies (HWPT) Engineered Membrane Separation (EMS~(TM)) method is an alternative biooxidation bleedstream treatment method. EMS~(TM) processing removes the multivalent base metals ions in an acid solution to small volume EMS~(TM) "concentrate" (typically 25 percent of the feed stream volume). The EMS~(TM) method coincidentally makes a "lean acid" EMS~(TM) "permeate" (typically 75 percent of the feed-stream volume). In general, EMS~(TM) processing enables 75 percent of he bleedstream volume to be recycled; allows up to 2/3 of the bleedstream acid to be recovered as a 10 percent solution; and delivers dissolved metals in a highly concentrated stream suited to a. metals recovery or b. reduced cost lime neutralization for a given metals precipitation relative to full bleedstream neutralization (typically a 30 percent lime use savings). Implicit in the recovery of process water for re-use and reduced reagent addition requirement for metals precipitation is a significant reduction in wastewater-sludge disposal facility size. The economics of the EMS~(TM) treatment of heap biooxidation bleedstreams are: 1. capital cost approx=