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4.2 Bulk chemical composition Table 3. Results of smile acid generation testing an the four Mayflower sludge samples. <br /> The bulk concentration of Al,Ca.Fe,Mn and Zn in the four Mayflower samples is summarized pate Pyritic Sulfate Residual Total AP NP NNP NPR <br /> in Table 2. The sludge-rich samples are characterized by elevated concentrations of all elements. pH S(%) S(%) S('/.) S(•/.) <br /> The 6-riser sample has higher concentrations of Al.Fe,Mn and Zn than the delta sample. The <br /> delta sample has elevated Ca relative to the 6-riser sample,possibly reflecting the fact that the 3-dam 9.0 0.23 0.83 0.33 1.39 17.5 36.0 18.5 2.1 <br /> delta was the primary location where lime-treated water entered Mayflower prior to 1995. (tailings-rich) <br /> Delta 9.0 <0.01 6.93 0.02 6.93 0.8 334.0 333.2 427.5 <br /> Table I. Mineralogical composition of the four Mayflower samples by XRD(Corbett 1997). (sludge-rich) <br /> 6-riser 8.8 <0.01 4.41 <0.01 4.42 0.3 375.0 374.7 1.200.0 <br /> Qtz Ms Ksp Ab Kool Cc Gyp En Fir Maly (sludge-rich) <br /> 3-dam MM M m m•tr er m-tr Jr - - it 5-dam 8.2 0.39 0.09 0.05 0.53 13.4 13.0 -0.4 1.0 • <br /> (tailings-rich) (tailings-rich) <br /> Delta it - -- -• -- To - MM m-M - Units for AP,NP end NNP ue tons(kiloton CeCOs. Values less than MDL arbitrarily taken as vaMDL. <br /> (sludge-rich) AP=acid potential,calculated a(sulfide S+residual S)031.25. <br /> NP-neutralization potential. <br /> 6-riser m - - - - m-M - MM m-M - NNP-net neutralization potential(NP-AP). <br /> (sludge-rich) NPR-neutralization potential ratio(NP/AP). <br /> 5-dam MM M M m-tr tr or - -• - - <br /> (tailings-rich) <br /> Total unidentified phases estimated u 3.10%. Sludge-rich samples ere sulfurlfate values,red by sulfide sulfur below the method detection limit(MDL) <br /> Qtz-quara Ms-muscovite.Ksp-orthoclase;Ab-albite Kaol-kaolinite;Cc=calcite;Gyp-gypsum; and moderate sud ,mantizion potential <br /> NIin lowrrespotential(AP)v nluer. Sludge samples <br /> En=euringitc;Fir-fluorite;Maly=molybdenite also have elevated neutral izazion pWrntial(NP)and s:omaponding elevated neutralization potential <br /> tr-trace(<3%);m-minor(3.10'A);M-moderate(10.30%);MM=major(>30'/.) ratios(NPR <br /> Tailings-rich samples are characterized by alkaline pale pH,but have elevated pyritic sulfur <br /> and low sulfate sulfur values compared to the sludge-rich samples. The low sulfate sulfur confirms <br /> The two relatively tailings-rich samples have lower concentrations of the five elements,with the the relative lack of a sludge component in these samples. The NPs of the tailings-rich samples are <br /> exception of elevated iron in the l-dam sample. On the basis of these data,the Mara sample at team one order of magnitude lower than those of the sludge-rich samples. The combination of <br /> appears to contain a higher proportion of sludge than does the 5-dam sample. elevated sulfide sulfur and low NP results in NNP and NPR values that are indicative of samples <br /> that could produce acid upon weathering. <br /> Table 2. Concentration of selected elements in Mayflower sludge samples. 4.3 Mineralogical composition and textural features of sludge-rich samples by electron • <br /> microprobe <br /> AI(mg/kg) Ca(mg/kg) Fe(mg/kg) Mn(mg/kg) Zn(mg(kg) <br /> 3-dam 5,410 17.100 26,500 309 Sig The two sludge-rich samples (delta and 6-riser) were submitted for analysis by electron <br /> (pilings-rich) microprobe. The analysis of the(-riser sample indicates the presence of ettringile,calcite,fluorite <br /> and an unidentified Ca-AI-Fe oxide/hydroxide phase. Ettringite makes up much of the sample <br /> Delta 39,900 260,000 20,600 8,970 3.950 matrix, although it is suspected of being at least partially amorphous,due to the fact that it <br /> (sludge-rich) appeared darker than expected in back$catler mode(Drosnahan 1997). The presence of poorly <br /> 6-riser 53,700 229,000 32,100 15,500 5,190 crystalline ettringile is also supported by the low intensity XRD peaks(Figures 3,4). Calcite <br /> occurs as subhedral grains that average several to's of microns in diameter. Fluorite is spherical <br /> (sludgo-rich) grains that average less than 5 microns in diameter. The unidentified Ca-AI-Fe oxide/hydroxide <br /> 5-dam 2,730 8,580 9,030 346 120 phase is present in significant quantities,and is presumed to be amorphous,since no such mineral <br /> (tailings-rich) was apparent in the XRD scans. Minor amounts of detrital quartz,muscovite,biotite,orthoclase <br /> and pyrite were also observed•and represent a small tailings component. <br /> The mineralogy of the delta sample differs somewhat from that of the 6-riser sample. Fluorite <br /> Static acid generation tests were performed on the four samples using the modified Sobck el al. was not encountered,although it war identified in the XRD scans(Corbett 1997). Calcite appears <br /> (1978)method where the sample is digested in HCI at ambient temperature for twenty-four hours to be less abundant in the delta sample,confirming the results of the XRD work. Again,much of <br /> prior to back-titration. Although the four samples have alkaline paste pH's,results demonstrate the sample matrix is composed of ettringite, at least some of which is amorphous• given the <br /> the different acid generating properties of the sludge-rich and tailings-rich samples(Table 3). combination of the dark appearance in backscatter made and the low,relatively broad XRD peaks. <br /> 652 653 <br />