Laserfiche WebLink
3422es_e.htm at mend20anrcan.gc.ca • Page 3 of 4 <br /> samples, indicating that all the sulphur present in these samples occurs as sulphate. <br /> Mineralogical analyses of all sludge samples showed a major amorphous phase. <br /> Readily leached metal species such as zinc were commonly associated with this phase, <br /> which appeared to be effective in scavenging metal species (Al, Cu, Fe, Mg, Na, Ni, <br /> Zn) during precipitation. Calcium is present as calcite, gypsum and bassanite; they <br /> occur both as individual grains and in the amorphous phase. The amount of calcite <br /> may indicate the degree of recrystallization and the increased stability of the sludges. <br /> Quartz, silicates, sulphides and iron oxide particles found in the sludges are detrital in <br /> origin. <br /> Sludge leachability <br /> AMID treatment sludge samples were leached using two protocols. The Ontario <br /> Leachate Extraction Procedure (LEP) uses an acetic acid solution as a leachant while <br /> the Modified LEP substitutes a synthetic acid rain for the acetic acid. Acetic acid <br /> mimics the organic acids expected to be present in a municipal landfill and assumes <br /> co-disposal of mineral processing and municipal wastes. On the other hand, the <br /> mixture of sulphuric and nitric acids better simulates the inorganic acids that are likely <br /> to come in contact, through acidic precipitation, with sludges disposed in ponds. <br /> Generally, less metal was leached from the sludges when they were subjected to the <br /> Modified LEP as opposed to the Ontario LEP. Sludge leachability is strongly <br /> dependent upon the final leachant pH which is influenced by the choice of leachant <br /> and by the neutralizing potential of the sludge. Metal leachability increases with <br /> • decreasing pH at pH less than about 9.5. The amount of metal leached is also related <br /> to the metal concentration in the sludge itself. In general, the aged sludge samples <br /> showed an increase in stability relative to the fresh samples as indicated by the <br /> leaching results and supported by the mineralogical data and particle size analyses. <br /> AMID treatment sludges are waste products which may be subject to waste <br /> management regulations. A leachate extraction test may be used to evaluate if the <br /> waste is capable of yielding a leachate which exceeds regulated concentration limits <br /> for selected contaminants. When a waste fails the test in relation to the limits specified <br /> in a particular jurisdiction, the waste may be classified as hazardous. All but two of the <br /> sludge samples subjected to the Ontario LEP passed the test when the leachate <br /> concentrations for metals are compared to the regulated limits governing the <br /> classification of hazardous waste material in Canadian jurisdictions. A fresh sludge <br /> from a base metal operation failed on zinc and an aged sludge from a uranium mine <br /> failed on uranium. There are only three jurisdictions in Canada which have a regulated <br /> limit for zinc and this sludge would actually fail only in comparison to Quebec's <br /> current regulation. It must be noted however, that Quebec's proposed new regulated <br /> limits do not include zinc. None of the sludge samples failed when tested with the <br /> Modified LEP. The leachate concentrations from both tests were generally at least five <br /> times lower than the most stringent of the regulated limits. <br /> Therefore, fresh AMD treatment sludges would not generally be classified as <br /> • hazardous wastes based on current leaching protocols and regulated contaminant <br /> limits. Aged sludges are even less likely to be classified as hazardous wastes. Based <br /> http://mend2000.nrcan.gc.ca/reports/3422es_e.htm 1/18/99 <br />