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MEASUREMENT AND QUANTIFICATION OF SULFATES IN MINING INFLUENCED WATER
Citation:
AL-ABED, S. R., D. J. REISMAN, AND V. SUNDARAM. MEASUREMENT AND QUANTIFICATION OF SULFATES IN MINING INFLUENCED WATER. Presented at Hard Rock 2006 Conference, Tucson, AZ, November 14 - 16, 2006.
Impact/Purpose:
To inform the public.
Description:
Most hard rock (mineral) mine drainages contain metals and sulfates higher than current water quality standards permit for discharge. In treating these wastes with passive systems, scientists and engineers have concentrated on using sulfate-reducing bioreactors (SRBRs) and their microbial consortium to produce sulfides to precipitate metals. Another advantage of using SRBRs is to reduce sulfate concentrations to meet discharge requirements. On many other current active mine water treatment systems, some type of chemical precipitation is being used to reduce only the metals leaving high sulfate levels untreated. Many of these sites have to treat millions of gallons of water in a shortened treatment season because of winter access issues at higher elevations. The lack of storage areas for the treated water at these sites means that there is little holding time allowed prior to release or discharge. In most of these cases, operators need to have a reliable and quick method for analyses of the treated mining influenced water (MIW) to ascertain if the sulfate concentrations are below the allowable discharge levels. Because of the high costs to have a chemist and a laboratory with expensive equipment on each of these sites, many of the operators and remedial site managers rely on the turbidimetric method (TM) to determine the sulfate level prior to deciding to discharge or to continue with more treatment. In this study, the TM, ion chromatography (IC), and inductively coupled plasma atomic emission spectrometry (ICP-AES) with and without acid digestion have been compared and validated for the determination of sulfate in mining wastewater. Analytical methods were chosen to compare the performance of a portable field turbidimetric instrument and to validate the underlying assumption utilized in conversion of total sulfur to sulfate during ICP-AES analysis. Accuracy and precision of analytical technques were compared to one another using control and field samples collected from a mine site using the Bonferroni multiple comparison statistical test. Effects of sample dilution, filter pore size and acidification on sulfate quantification were also studied. We will present results from this study to show that the performance of the turbidimetric method was affected significantly by sample dilution and acidification, and also revealed poor sulfate recoveries for control samples ranging from 0% to 83.5%. The analytical method had significant effect (p<0.0001) on the sulfate quantification. Our results also show that the use of the turbidimetric method, especially when dilutions are used, may produce inaccurate sulfate levels and thus it may not be used for decision-making purposes.