Current state of fine mineral tailings treatment: A critical review on theory and practice

The mining industry produces fluid fine mineral tailings on the order of millions of tonnes each year, with billions of tonnes already stored globally. This trend is expected to escalate as demand for mineral products continues to grow with increasingly lower grade ores being more commonly exploited by hydrometallurgy. Ubiquitous presence and enrichment of fine solids such as silt and clays in fluid fine mineral tailings prevent efficient solid-liquid separation and timely re-use of valuable process water. Long-term storage of such fluid waste materials not only incurs a huge operating cost, but also creates substantial environmental liabilities of tailings ponds for mining operators. This review broadly examines current theoretical understandings and prevalent industrial practices on treating fine mineral tailings for greater water recovery and reduced environmental footprint of mining operations

A critical evaluation of the multi-item microbial challenge test in ophthalmic disinfectant testing

The Multi-item Microbial Challenge Test (MIMCT) is a stringent, carrier assay of the disinfecting efficacy of a contact lens care regimen. The test involves four steps: 1) in vitro contamination of contact lenses in the presence of organic load; 2) cleansing the contact lens by mechanical rubbing and subsequent rinsing; 3) disinfection of the cleansed lens; and 4) assaying the contact lens and the disinfecting solutlon for viable mlcroorganlsms. The variability of the Individual steps was evaluated in this study by the Contributions of Elements protocol. The eff icacy of the cleanslng step, whlle reputed to be highly variable, was found to be reproducible and dependent upon the formulation under test. A contact lens disinfecting reglmen must reduce the level of contaminants to approximately l(r CFUnens to enjoy a 95% chance of passing the MIMCT. Thls reflects a 10-log unit reduction from the initial inoculurn of approximately 1CP CFUnens. The stringency of the MIMCT depends on the ability of the recovery system to allow the growth of low numbers of residual challenge microorganisms in the presence of the disinfecting solution. Neutralizers included In the recovery system to lnhlblt the disinfectant are therefore critically important to the stringency of the assay. The design of experiments to evaluate neutralizers speclflcally for the MlMCT Is discussed with suggestions for an improved procedure. Introduction Passing the Multi-item Microbial Challenge Test (MIMCT) is accepted as evidence of a contact lens chemical disinfectionregimen'sefficacy. This test examines the ability of a specific regimen to disinfect a contact lens in the presence of organic load. The test consists of several sequential steps designed to emulate standard contact lens cleaning.(rub and rinse) and disinfection. The lens. with an organic load, is inoculated with high concentrations of microorganism The contaminated lens is then subjected to a regimen that can consist of manual rubbing (cleaning), rinsing, chemical disinfection, and, if necessary, a final rinse. The initial cleaning removes particulate debris from the surface of the lens and may significantly reduce the number o