General Information
Abstract: In 2001, a project was initiated to stduy the behavior of treatment sludges in northern climatic conditions. For this study, leach columns were commissioned in the laboratory to evaluate metal mobility from treatment sludges. In addition, sludge densification by the freeze-thaw mechanism was studied.
Sludge samples from effluent treatment operations at United Keno Hill (UKH) and Faro mine sites were used in this study. This project has been divided into two main tasks; a leaching study and a freeze-thaw study, but conducted in the laboratory and in the field. This final report presents the results of the sludge characterization, the freeze-thaw study and the leaching study.
The composition of the acid mine drainage sludge produced at Faro and UKH mine sites were different as compared to typical lime treatment sludge. The metal composition of the mine water was very low, in particular for iron. While the pH of the wastewater was near neutral, the addition of lime was required mainly to precipitate zinc. The metal content of the sludge was low and the neutralization potential was very high which was in accordance with the high carbonate content measured in the sludge. The United Keno Hill sludge was mainly composed of calcite. Instead of calcite, the Faro sludge had as a major consituent aragonite, a pseudomorph of calcite crystals.
The sludge characterization revealed that the lime treatment process at both sites could be optimized. The origin of the high carbonate content of the sludge was probably from the lime quality used and from a high carbonate concentration in the mine water. Mineralogical results revealed evidence that minor amounts of calcium carbonate is from primary precipitation during the lime addition. Also, larger particles of calcium carbonate were also identified in both sludges which are thought to be from the lime used to precipitate metals. The lime treatment process could probably be improved by optimizing the slaking temperature, agitation time rate and using the proper chemical reagents to precipitate metals.
The freeze-thaw mechanism evaluated in the field increased the percent solids of the sludge fromm 23% to 60% for the UKH and from 28% to 58% for the Faro sludge. The freeze-thaw study conducted in the laboratory showed final percent solids values in the same order. The capability of the sludge to dewater so easily is explained by the low amount of iron hydroxide in the sludge. Because no particle repulsion force or bond water are associated to the iron hydroxide phase. The high solids content reached in this study was mainly due to natural dewatering rather than the freeze-thaw mechanism.
In terms of chemical stability, the column and the SPLP studies revealed that the metal release in minimal because of the high neutralization of both sludges. The variation of the temperature did not have any significant impact on metal mobility. Nickel and zinc were released to significant levels for both sludges when the sludges were subjected to the TCLP.
Sludge samples from effluent treatment operations at United Keno Hill (UKH) and Faro mine sites were used in this study. This project has been divided into two main tasks; a leaching study and a freeze-thaw study, but conducted in the laboratory and in the field. This final report presents the results of the sludge characterization, the freeze-thaw study and the leaching study.
The composition of the acid mine drainage sludge produced at Faro and UKH mine sites were different as compared to typical lime treatment sludge. The metal composition of the mine water was very low, in particular for iron. While the pH of the wastewater was near neutral, the addition of lime was required mainly to precipitate zinc. The metal content of the sludge was low and the neutralization potential was very high which was in accordance with the high carbonate content measured in the sludge. The United Keno Hill sludge was mainly composed of calcite. Instead of calcite, the Faro sludge had as a major consituent aragonite, a pseudomorph of calcite crystals.
The sludge characterization revealed that the lime treatment process at both sites could be optimized. The origin of the high carbonate content of the sludge was probably from the lime quality used and from a high carbonate concentration in the mine water. Mineralogical results revealed evidence that minor amounts of calcium carbonate is from primary precipitation during the lime addition. Also, larger particles of calcium carbonate were also identified in both sludges which are thought to be from the lime used to precipitate metals. The lime treatment process could probably be improved by optimizing the slaking temperature, agitation time rate and using the proper chemical reagents to precipitate metals.
The freeze-thaw mechanism evaluated in the field increased the percent solids of the sludge fromm 23% to 60% for the UKH and from 28% to 58% for the Faro sludge. The freeze-thaw study conducted in the laboratory showed final percent solids values in the same order. The capability of the sludge to dewater so easily is explained by the low amount of iron hydroxide in the sludge. Because no particle repulsion force or bond water are associated to the iron hydroxide phase. The high solids content reached in this study was mainly due to natural dewatering rather than the freeze-thaw mechanism.
In terms of chemical stability, the column and the SPLP studies revealed that the metal release in minimal because of the high neutralization of both sludges. The variation of the temperature did not have any significant impact on metal mobility. Nickel and zinc were released to significant levels for both sludges when the sludges were subjected to the TCLP.
Authors: Jean-Francois Fiset, Janice Zinck and Gilles Laflamme (Natural Resources Canada)
Map Scale: 1 : 0
Citation: Jean-Francois Fiset, Janice Zinck and Gilles Laflamme (Natural Resources Canada), 2003. Mine Sludge Stability - Densification in Cold Climates. Mining & Petroleum Environment Research Group, 2003-4.
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