THE EFFECTIVE TREATMENT OF ACID MINE WASTES BY A
LOW PRESSURE CHARGED MEMBRANE ULTRAFILTRATION PROCESS
D. Bhattacharyya, Associate Director
S. Shelton, Graduate Student
R. B. Grieves, Chairman
Department of Chemical Engineering
University of Kentucky
Lexington, Kentucky 40506
INTRODUCTION
Acid mine water is a problem of critical significance in most of the coal producing
regions.    The construction of coal conversion plants will produce a greatly increased
demand for both coal and water and will provide a great impetus for the recycle and
reuse of treated acid mine drainage water.   Acid mine water is produced by oxidation
and hydrolysis of pyrite (FeS2) exposed during coal mining.   The resulting acid water,
containing H2S04, Fe2+, and Fe3  , dissolves various metals (Ca, Mg, Al, Mn, etc.)
from the surrounding strata and produces highly contaminated water containing S042',
H+, Ca2+, Mg2+, Mn2+, Al3+, Fe2+, Fe3+, and other heavy metal ions.
Charged membrane ultrafiltration provides a unique and broadly applicable technique
for the simultaneous separation of various inorganic metal ions (including precipitates)
present in industrial wastewaters.   Negatively charged, anisotropic, non-cellulosic membranes (10 x 10"8 cm to 20 x 10"8 cm pore widths) provide high water flux and
adequate rejections of metals (and sulfate) at low transmembrane pressures (5 x 10s
N/m2 to 7 x 10s N/m2).   This process is particularly appropriate for applications requiring water reuse in which completely demineralized water is not warranted.
Bhattacharyya et al. have demonstrated promising ultrafiltration results with electroplating rinse waters [1], waters of high hardness [2], complex wastewaters containing
organic and inorganic solutes [ 3 ], and non-ferrous metal production wastewaters containing high concentrations of heavy metals [4],   Sachs [5] and Mizrahi et al  [6]
have used charged membranes with primary and secondary sewage effluents and obtained
good water flux at low pressures.
The separation of ionic solutes by charged ultrafiltration membranes is due to repulsion of coions by the fixed charged groups in the membrane skin.   The attainment
of adequate separation at low pressure without membrane compaction problems and the non-
fouling nature with solutions containing high concentrations of suspended solids are
attractive features of charged membranes.   These membranes are primarily suitable for
dilute to moderately concentrated solutions of low effective osmotic pressures.   Reverse
osmosis membranes (operated at pressures above 3 x 106 N/m2), in contrast, are used
for water desalination and/or for wastewaters of high osmotic pressures for which very
high rejections (98.0 to 99.9%) of all inorganic ions are desired.
The treatment of acid mine waters by charged membrane ultrafiltration for the
purpose of water reuse is a very promising application.   Most physicochemical treatment
methods reported in the literature are primarily directed towards removal of acidity and
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