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Characterization and Settling of Solid Contaminants in Coal Mine Effluent
Author(s) -
Zhou Z.,
Bateman J. C.,
Babchin A.,
Bird G. W.
Publication year - 1994
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1994.00472425002300040019x
Subject(s) - settling , gypsum , flocculation , effluent , chemistry , sediment , suspended solids , mineralogy , environmental engineering , environmental chemistry , wastewater , geology , environmental science , materials science , metallurgy , paleontology
Groundwater and runoff water at surface coal mines are often contaminated with suspended solids and should be treated before it is discharged to surface water bodies. The suspended solids in the waste effluent of the Highvale mine, Alberta, Canada, are dominantly micron and submicron sized, dioctahedral smectite. They form stable colloidal suspensions in sodium bicarbonate solutions. Theoretical consideration suggests that the suspended smectite can be flocculated by divalent cations such as Ca 2+ . Experimental results show that even a small amount (2.7 m M ) of gypsum can flocculate the system and cause clays to settle. Depending on the solution composition, up to 85% of the effluent volume can be reduced after 24 h settling. The clay settling rate is affected by both NaHCO 3 and gypsum concentrations. Without gypsum addition, no settling occurs regardless of NaHCO 3 concentrations (2 to 30 m M ). At a fixed NaHCO 3 concentration, clay settling rate increases with an increase in gypsum concentration. At a fixed gypsum concentration, the rate of clay settling decreases with an increase in NaHCO 3 concentration. The initial settling rate (ISR) can be correlated to the equivalent fraction of Na + on the clay surface ( E Na ) or the exchangeable sodium percentage (ESP) on the smectite surface. Linear regression of the experimental data gives an empirical equation ISR = −0.170 − 0.459 log( E Na ) with a regression coefficient of 0.917, where E Na = ESP/100. The functional relation between solid settling rate and ESP can be useful in the design of sediment ponds for treatment of coal mine effluent.