Effect of tailings properties on paste backfill performance

Transcription

1 Effect of tailings properties on paste backfill performance M. Fall*, M. Benzaazoua, S. Ouellet University of Quebec in Abitibi-Temiscamingue, Canada The increasing use of paste backfill in underground mining makes it necessary to quantify the effect of tailings properties, such as physical and chemical properties, on the performance properties of cemented paste backfill (CPB). Hence, this paper presents the results of an experimental investigation carried out to evaluate the influence of physical (tailings particle size and density) and chemical properties (tailings sulphide content) of tailings on the performance properties of the paste backfill. The studied performance properties included: mechanical and economical performance, water demand, pulp density and transportability. The gained results have shown that the tailings fineness and density influence significantly the performance properties of paste backfill. The sulphide content of the tailings has also significant effect on the performance of paste backfill. The results of this study will contribute to better understand the behaviors of the paste backfill and optimize its mixtures. 1 INTRODUCTION The use of paste technology for underground backfill has been accepted as a cost-effective alternative to rock and hydraulic backfill worldwide in the mining industry. Its using is extensive in Canadian underground hard rock mines and follows an increasing trend as well as in many parts of the world. The application of paste backfill leads to a significant reduction of cyclical nature of mining, improves ground conditions, ensures the stability of the underground excavations, speed up production and greatly reduces environmental costs (Hassani and Bois, 199). Additionally, paste backfill applications, known to allow enhanced disposal of large fractions of fine tailings that have traditionnaly required permanent surface disposal and management, offer other significant environmental and cost benefits for mines (Archibald et al, 199). However, despite extensive use of this relatively new technology, all effects of tailings properties on paste backfill are not fully known. Only a few works (Landriault et al. 1997, Benzaazoua et al. 3; Fall and Benzaazoua 3a, Kesimal et al. 3) have shown that the tailings particle size can influence the strength of the hardened paste backfill. But these works only briefly described the influence of tailings particle size on CPB uniaxial compressive strength (UCS). They had no information on the effect of tailings particle size on all of the most important quality criteria for backfill. They also did not account for the influence of tailings density and sulphide contents. Hence, cooperative research studies were conducted by the above authors with several Canadian underground hard rock mines currently using cemented paste backfill to investigate the effect of the physical and chemical properties of tailings on paste backfill as well as to optimize the desliming of mill tailings. This paper presents the results of the experimental part (Fall et al. a) of these research studies. Thus, the main purpose of this experimental study was to evaluate the influence of tailings fineness and density on the performance properties of the paste backfill, and to study the effect of the amount of sulphide minerals contained in the tailing on the quality of the paste backfill. The studied performance properties included the strength, cost and microstructure of the hardened paste backfill and the water demand for the fresh paste backfill. The reactivity of the sulphide minerals present in the tailings was also evaluated. EXPERIMENTAL PROGRAM.1 Materials The materials used included: binder reagents (Portland cement type I blended with Portland cement type V in the ratio 5/5, and Portland cement type I blended with Slag in the ratio /), waters (tap waters) and tailings. The tailings materials used in this study were collected from three mines in eastern Canada (Mines A, B and C). Mine A is a gold mine and Mines B and C are polymetallic. The sulphur content in tailings from mine A (TA) is lower than 3 % and the tailings of mine B (TB) and C (TC) contain respectively 15 % and % (in weight) sulphur (table 1). The sulphur is mainly due to the presence of pyrite (FeS ). *Corresponding author: Dr. Mamadou Fall; URSTM University of Quebec in Abitibi-Temiscamingue; 5, boul. de 1 l Université, Rouyn-Noranda Qc, J9X 5E Canada; mamadou.fall@uqat.ca

2 Table 1. Main chemical elements present in the sampled tailings materials* Element Al As B Bi Ca Si Cu Fe Mg Mn Na Pb S Zn Unit wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % wt % Tailings Mine A TA TA TA Tailings Mine B TB Tailings Mine C TC *Chemical composition determined by ICP ES analysis To obtain tailings particle size distributions belonging to coarse, medium and fine tailings, the sampled tailings had to be reprocessed. This was done by separation of TA by hydrocyclone and sieving (elimination the coarse tailings particles) and of TB and TC by hydrocyclone, creating several grain size classes corresponding to fine, medium and coarse tailings. The particle-size distributions of the fabricated tailings are shown in figure 1. Table gives the physical characteristics of the tailings used in this study. Analysis of the particle size distributions of tailings TA-1 to TA-5 reveals that these latter had different uniformity coefficients of between 7 and 1, different proportions of fines and similar coefficients of curvature. Based on both the coefficients of uniformity and curvature, tailings TA-1 to TA-5, these can be classified as well-graded tailings. However, the coefficient of uniformity is strongly influenced by the proportion of fines (table ). High proportions of fines leads to a more uniform tailings particle size distribution, i.e. reduces the grading of the tailings. Regarding the tailings TB1 to TB-5, the most significant differences between the fabricated tailings samples are the proportion of fines. Tailings TB-1 to TB-5 are well graded and have similar coefficients of uniformity and curvature. Decreasing the fines content slightly leads to better graded tailings. Since the density of tailings materials is strongly dependant on the sulphur content (Brakebusch, 199, Fall and Benzaazoua, 3b), the desulphurization (McLaughin and Stuparyk, 199, Stuparyk et al. 199, Leppinen et al., 1997, Benzaazoua et al., etc.) process was used to prepare tailings materials with different densities. Desulphurisation allowed us to create five different tailings (TB-5 to TB-1) from the TB samples that differ only by density (table ). The sulphur content of the prepared tailings TB-5, TB-, TB-7, TB-, TB-9, TB-1, was respectively approximately %, %, 1 %, 1 % and 39 % (by weight). Volume percent (cumulative) Grain size (µm) Figure 1. Particle size distribution of the tailings materials used

3 Table. Physical properties of the sampled and fabricated tailings samples ρt (g/cm³) D1 (µm) D5 (µm) D (µm) D9 (µm) C u C c (< µm) Tailings Mine A TA-1 sampled TA- sampled TA-3 sampled TA- prepared TA-5 prepared Tailings Mine B TB sampled TB-1 prepared TB- prepared TB-3 prepared TB- prepared TB-5 prepared TB- prepared TB-7 prepared TB- prepared TB-9 prepared TB-1 prepared Tailings Mine C TC sampled TC-1 prepared TC- prepared Cu: coefficient of uniformity; Cc coefficient of curvature; ρ t: tailings density. Paste backfill mix proportions and testing methods The paste backfill mixtures, presented in table 3, were prepared to study the effect of tailings fineness on the properties of cemented paste backfill (CPB). All of the cylinders were filled with backfill material and some paste backfill cylinders (mixes names with D termination; D meaning drained) were punched at their bases to study the effect of drainage according to tailings fineness on porosity of the fresh paste backfill and the consequence on the CPB properties. All of the mixtures had a slump value of 1 cm or seven inches. 1 paste backfill samples were produced and the water demand (pulp density, W/C ratio) necessary to reach a slump value of 1 cm was evaluated. After curing times of 1,, 5, 9 days, the uniaxial compressible strength, the void index and total porosity of each backfill sample were determined. MIP-tests were done on paste backfill specimen (after a curing times of days) made from tailings TA to evaluate the pore size distribution. To study the effect of the tailings density on the different properties (UCS, cost) of the cemented paste backfill, the tailings TB- to TB-1 were considered as base tailings for the backfill mixtures. The latter differed only by their densities (except of TB-1, which is slightly finer). The rinsing of the tailings materials (with tap water) flushed out the sulphate present in the tailings. These tailings were used to make about paste backfill specimen with blended cements PCI/PCV and PCI/Slag ratios as given in table. The UCS of the paste backfill samples at different curing times ( and 9 days) and binder consumption expressed in % volume as well as the corresponding binder costs were evaluated. 3

4 Table 3. Mix design for evaluation of the effect of tailings fineness on paste backfill properties (Fall et al. a) Mixes name Binder Tailings Mixing water Slump Types Ratio % wt Name density % fine (cm) MTA-1-V PCI / PCV 5/5.5 TA Tap water 1 MTA--V PCI / PCV 5/5.5 TA-. Tap water 1 MTA-3-V PCI / PCV 5/5.5 TA Tap water 1 MTA--V PCI / PCV 5/5.5 TA-. Tap water 1 MTA-5-V PCI / PCV 5/5.5 TA-5. 5 Tap water 1 MTA-1-S PCI / Slag /.5 TA Tap water 1 MTA--S PCI / Slag /.5 TA-. Tap water 1 MTA-3-S PCI / Slag /.5 TA Tap water 1 MTA--S PCI / Slag /.5 TA-. Tap water 1 MTA-5-S PCI / Slag /.5 TA-5. 5 Tap water 1 MTA-1-V-D PCI / PCV 5/5.5 TA Tap water 1 MTA-3-V-D PCI / PCV 5/5.5 TA Tap water 1 MTA-5-V-D PCI / PCV 5/5.5 TA-5. 5 Tap water 1 MTA-1-S-D PCI / Slag /.5 TA Tap water 1 MTA-3-S-D PCI / Slag /.5 TA Tap water 1 MTA-5-S-D PCI / Slag /.5 TA-5. 5 Tap water 1 MTB-1 PCI / Slag /.5 TB-1 3. Tap water 1 MTB- PCI / Slag /.5 TB Tap water 1 MTB-3 PCI / Slag /.5 TB-3 3. Tap water 1 MTB- PCI / Slag /.5 TB Tap water 1 MTB-5 PCI / Slag /.5 TB Tap water 1 *Chemical composition determined by ICP ES analysis Table. Mix design for evaluation of the effect of tailings density on paste backfill properties Binder Tailings Mixing water Slump (cm) Mixes name Types Ratio % wt Name density % fine MTB- PCI / PCV 5/5.5 TB-.9 5 Tap water 1 MTB-7 PCI / PCV 5/5.5 TB Tap water 1 MTB- PCI / PCV 5/5.5 TB Tap water 1 MTB-9 PCI / PCV 5/5.5 TB Tap water 1 MTB-1 PCI / PCV 5/5.5 TB-1. Tap water 1 MTB- PCI / PCV 5/5.5 TB-.9 5 Tap water 1 MTB-7 PCI / Slag /.5 TB Tap water 1 MTB- PCI / Slag /.5 TB Tap water 1 MTB-9 PCI / Slag /.5 TB Tap water 1 MTB-1 PCI / Slag /.5 TB-1. Tap water 1 To study the effect of the tailings sulphur content on paste backfill properties (strength, durability) and the reactivity of the sulphide minerals within the non cemented tailings and the cemented paste backfill, the tailings TB-11 to TB-1 containing different amounts of sulphur (%, %, 1%, 1%, 39%) were used to made backfill specimen with blended cements PCI/PCV and PCI/Slag ratios as given in table 5, as well as to fabricate specimen only made from tailings material with different sulphur and degrees of water saturation. The UCS of the paste backfill samples at different curing times ( and 9 days) and binder consumption expressed in % volume as well as the corresponding binder costs were evaluated. Oxygen consumption tests (Elberling et al. 199, Elberling et Nicholson 199) were performed on both paste backfill specimens and non cemented tailings specimens to evaluate the reactivity of the sulphide minerals (pyrite) within these specimens. The experimental program for the oxygen consumption tests carried is described in detail in Ouellet et al. 3 and Benzaazoua et al. 3a.

5 Table 5. Mix design for evaluation of the effect of tailings sulphur content on paste backfill properties, and of the reactivity of the sulphide minerals within the paste backfill Binder Tailings Mixing water Slump (cm) Mixes name Types Ratio % wt Name density % fine % sulphur MTB-11 PCI / PCV 5/5.5 TB Tap water 1 MTB-1 PCI / PCV 5/5.5 TB Tap water 1 MTB-13 PCI / PCV 5/5.5 TB Tap water 1 MTB-1 PCI / PCV 5/5.5 TB Tap water 1 MTB-15 PCI / PCV 5/5.5 TB Tap water 1 MTB-1 PCI / PCV 5/5.5 TB Tap water 1 MTB-17 PCI / Slag /.5 TB Tap water 1 MTB-1 PCI / Slag /.5 TB Tap water 1 MTB-19 PCI / Slag /.5 TB Tap water 1 MTB- PCI / Slag /.5 TB-. 39 Tap water 1 3 RESULTS AND DISCUSSIONS 3.1 Effect of physical properties of tailings on paste backfill performance Effect of tailings fineness on the microstructure of paste backfill The main results of the effect of tailings fineness on the microstructure of paste backfill are presented in figure to 3. From this figure, it is clear that the proportion of fine tailings (<µm), i.e., the fineness of the tailings materials used in the sample mixture strongly influence both the overall porosity of the cemented backfill material (figure ) and the pore size distribution within it (figures -3). The finer the tailings material used, i.e., the greater the proportion of fine tailings particles, the greater the overall porosity of the backfill becomes. Figure shows that the total porosity of all of the paste backfill samples decreases as the proportion of fine particles (< µm) in the tailings material decrease. However, the extent of the porosity decrease is variable, i.e., depends on fines content. The decrease in porosity with the decrease in the fines content is greater for paste backfill made of fine (fines < %) or medium (fines: -35%) tailings than those made from coarse tailings. Figure shows also the microstructure (total porosity and void ratio) of the paste material is strongly influenced by the drainage ability of the fresh backfill. The drained paste backfill samples show both less porosity and smaller void ratios. As shown in Benzaazoua et al. (3), paste backfill mixes made from coarse tailings (MTA-5-V-D or MTA-5-s-D) loose more water (by drainage) than those made from fine tailings material (case of MTA-1-V-D or MTA-5-S-D). This water loss leads to the settling of the paste backfill (increasing of the packing density) and the consequent reduction of total porosity and void ratio of the backfill material. These observations are in substantial agreement with earlier experimental investigations about CPB drainage ability performed by Belem et al. (). Figure 3 also shows that the paste backfill specimens are characterized by two distinct pore size distributions, notably pore diameters between.5-1µm and pore diameters between 1-1 µm. The contribution of pore diameters smaller than.5 µm or greater than 1 µm to overall porosity is low. The distribution of the two main pore diameters is significantly influenced by the proportions of fine tailings particles. While the pore diameters between.5 and 1µm are relatively well represented in the samples made from fine and medium tailings, their volume is small in backfill samples made from coarse tailings (figure 3). Indeed, it can be observed in figures 3, that decreasing of proportion of fines in the tailings is associated with a decreasing of the volumes of pores with diameter smaller than 1 µm (figure 3). The volume of macropores > 1 µm is greatest in paste backfill samples made from tailings containing only 5 % of fines particles (coarse tailings). This may have effect on paste backfill strength gain. 5

6 (a) Void ratio (e) e- days-pci/pcv e- days-pci/slag e- days-pci/pcv-drained e- days-pci/slag-drained n- days-pci/pcv n- days-pci/slag n- days-pci/pcv-drained n- days-pci/slag -drained % 5% 5% 5% 5% 5% % % % % % Porosity (n) (b) Void ratio (e) e- days-p CI/Slag n- days-p CI/Slag 5% 5% 5% 5% % % % %. % Figure. Effect of tailings fineness on void ratio and total porosity on paste backfill samples made from tailings TA (a) and TB (b) (after days curing). (Fall et al. a) Porosity (n) 1 75% 1 % % Pore diameter (µm) Pore diameter (µm) 1 55% 1 5% Pore diameter (µm) Pore diameter (µm Figure 3. Effect of tailings fineness on pore size distribution of paste backfill specimens cemented with PCI/PCV after days of curing (tailings sample TA). reached, at which point it remains constant (figure 3.1. Effect of tailings fineness on paste a) or begins to slowly decrease (figure b) with backfill strength development decreasing grain fineness. These observations can be attributed to the influence of the tailings Figure show the compressive strength fineness on the overall porosity of the paste development of the paste backfill related to the size backfill as well as to the effect on the pore size of the tailings fineness. It points out that the distribution within it (figures -3), and to the proportion of fines (< µm) in the tailings influence of the tailings particle size on the specific materials has a strong influence on the strength surface of the tailings material. gain of the CPB. It can also be noted that coarse Indeed, from a fines content of -9 wt. % to and medium tailings are more favorable for paste coarse tailings with a fines content of 5 and 35 backfill strength gain. A CPB made of fine tailings wt. %, there is a grading improvement of the generates lower strength. Figure also indicates tailings particle sizes distribution (table and that, for the undrained paste backfill samples, the figure 1). This leads to a decrease of the void UCS increases as the grain fineness decreases until spaces between the tailings particles and approximately % of the fines content was consequently, to lower porosities or void spaces within paste backfill as shown in figure. This

7 decreasing porosity or void spaces thus causes an increase in paste backfill strength. However, decreasing the porosity of the backfill with a decrease in the proportions of the fines tailings particles (< µm) is not the only parameter responsible for the variation in backfill strength. Indeed, it can not explain the slight decrease of backfill strength for a fines proportion of 3-5 %. Analysis of figure 3 shows that the pore size distribution within the paste backfill, particularly the proportions of macropores with diameter between 1-1 µm, seems to play a significant role in the strength gain of paste backfill. As observed in figure 3 and, at 5 % fines content, the proportions of macropores 1-1 µm within the paste backfill increases drastically. This higher proportion of macropores (1-1 µm) may have caused the small decrease of the strength for paste backfill made from coarse tailings (5 % fines) compared to backfill specimens made from tailings containing 5 to % fines particles. Thus, it can be concluded that not only does the overall porosity influence the strength of the paste backfill, but the pore size distribution, which is largely governed by the proportions of fine particles present in the tailings material, also plays a decisive role in the strength development of the cemented backfill. In addition to the effect of overall porosity and pore size distribution on the backfill strength gain, the finer particles increase the specific surface of the tailings materials and thus increase the surface area that must be cemented, since the cement coats the surface of the tailings particles. This also contributes to strength decrease of the paste backfill (figure, Fall et al. a) with increased tailings fineness. From figure a, it can be observed that the drained paste backfill samples show higher strength than the undrained samples. This may be attributed to the fact that drainage of the excess water in the fresh paste backfill leads to the settling of and higher packing density of the backfill. This causes a reduction in the total porosity and void ratio of the backfill material and consequently, to higher strength. Additionally, the drainage of the excess water affects positively the cement hydration (Benzaazoua et al. 3b). From figure, it can also be clearly seen that the fineness of the tailings strongly influences the rate of backfill strength gain at early stage (up to days curing). Paste backfill mixes made from coarse tailings (low proportion of fines) gain strength faster than those made from fine tailings (high proportion of fines). This is caused by the fact, that for a given W/C, the volume of void spaces between the tailings particles to be filled by the cement hydration product is smaller in the paste backfill specimens made from coarser tailings (lower porosity) than those made from finer tailings material. UCS (kpa) (a) UCS (kpa) PCI/PCV - 1 days PCI/Slag - 1 days PCI/PCV - days PCI/Slag - days PCI/PCV - 5 days PCI/Slag - 5 days PCI/PCV - days (drained) PCI/Slag - days (drained) Mine A : Gold tailing UCS days-pci/slag UCS 9 days-pci/slag M ine B : Polymetallic tailing (b) Figure. Effect of proportion of fines in the tailing on strength development of cemented paste backfill Effect of tailings fineness on water requirement of the fresh paste backfill Figure 5 shows the effect of the tailings fineness on the water/cement ratio and pulp density of cemented paste backfill. It can be noted that W/C of the paste backfill increases with the grain fineness of the CPB. For a given slump, the pulp density of the CPB decreases as the fineness of the tailings increases. This means fine tailings require more water for a given consistency than medium and coarse tailings. The influence of tailings particle size on water demand comes from the fact that the cement paste in its function as an adhesive, coats the surface of all tailings particles. Finer particles mean that there is more surface area to be 7

8 wetted, which in turn yields both higher moisture levels and lower densities for a given consistency. Additionally, since the overall porosity and void ratio of the paste backfill decreases from fine to coarse tailings, for a given total weight of tailings and cement, coarse tailings require less water than medium or fine tailings to reach the same consistency or pulp density. The comparison of figure and 5 indicates that the optimal W/C ratio to produce paste backfill with high strength is dependent on the fineness of the used tailings materials weight). This increasing in UCS with the tailings density is due to higher binder consumption in volume, as shown in figure 7. The latter puts into relief that, the higher the density of the tailings, the higher the binder consumption (in volume), i.e. the more expensive the backfill becomes. These results clearly demonstrate that the evaluation of the binder content of the CPB by weight percent, as commonly used in the mining industry does not show the real binder consumption of the paste backfill, in cases where the density of the mill tailings strongly vary. They also demonstrate the economic significance of using tailings with low sulphide content (tailings sulphide content can be reduced by desulphurization) for paste backfill design, since high sulphide contents lead to higher tailings density and consequently, to more expensive paste backfill. W/C 1 UCS days -PCI/PCV UCS days -PCI/Slag (a) Mine A - PCI/PCV Mine A- PCI/Slag Mine B -PCI/Slag 1 UCS (kpa) UCS 5 days -PCI/PCV UCS 5 days -PCI/Slag Pulp density (%) Mine A - PCI/PCV Mine A- PCI/Slag Mine B -PCI/Slag 1 (b) Figure 5. Influence of fine content on W/C ratio and pulp density of the fresh paste backfill (binder content.5 %) for a slump of 1 cm 3.1. Effect of tailings density on strength and binder consumption of the paste backfill Figure shows that, for a given curing time, there is a relationship between the strength and the density of the tailings materials used. It can be observed that increasing of the tailings density (from G s = 3.) gives the paste backfill a higher strength for the same binder proportion (.5% in Tailings specific gravity (G s) Figure. Effect of tailings density on UCS of on paste backfill samples made from TB (.5 %, binder content by weight) binder consumption (% volume) % vol. PCI/PCV % vol. PCI/Slag PCI/PCV -Cost PCI/Slag-Cost Tailings density (g/cm³) Figure 7. Relation of binder consumption and cost of the paste backfill (TB used) to density of the used tailings (.5 %, binder content by weight) (Fall et al. a) Binder cost ($/m³)

9 3. Effect of chemical properties of tailings on paste backfill performance The results of the effect of tailings sulphur content on paste backfill performance properties have shown that the sulphur has double effect (physical and chemical effect) on paste backfill properties. The first effect is physical. Indeed, increasing of the sulphur content in the tailings give the latter higher density. This leads to paste backfill with higher strength (figure ) due to the higher binder consumption in volume. UCS (kpa) UCS 1 days UCS 5 days Density UCS days UCS 1 days %wt Sulphur Figure. Effect tailings sulphur content (in weight percent) on the tailings density and strength development of paste backfill (cemented with PC I/PC V in the ratio 5/5). The second effect is chemical. As shown in figure, high sulphur content (39 % sulphur) in the paste backfill leads after 1 days to strength loss of the paste backfill. This is caused by sulphate attack. This raised the following question: Is the sulphides oxidation within the cemented paste backfill possible? The results of oxygen consumption tests (Benzaazoua et al. 3a, Ouellet et al. 3) (figure 9 and 1) bring some elements of response to this question. Indeed, figure 9, which represents the oxygen consumption (ie reactivity of the sulphide minerals in CPB) of cemented paste backfill, shows that the amount of consumed oxygen depends on the sulphur content, and the reactivity of the paste backfill specimens (except CPB made from tailings with 39% sulphur) does not significantly increase after days of curing time. The reactivity of the sulphide minerals in the cemented paste backfill are low compared to this in the non cemented tailings (figure 1). This low reactivity can be attributed to the fact, that the cemented paste backfill is water saturated. This Tailings density (g/cm³) high water saturation limits the diffusion of oxygen through the cement matrix and consequently its availability for oxidation reactions. Figure 1 puts in relief the relationship between the degree of water saturation and the sulphide reactivity in non cemented tailings. It can be observed, that at high water saturation (Sr.>5 %), the reactivity of the sulphides mineral in the non cemented tailings become as low as in cemented paste backfill. mol O/m /year % sulphur % sulphur 1 % sulphur 1 % sulphur 39 % sulphur 1 Time (days) Figure 9. Oxygen consumption of the paste backfill cemented with PCI/PCV in the time related to the sulphur content of the tailing. Mole O/m /year Sr (%) 7 9 % sulphur % sulphur 1% sulphur 1% sulphur 39% sulphur Figure 1. Oxygen consumption of the non cemented tailings related to their degree of saturation (S r ). CONCLUSIONS The objective of this study was to study the effects of the physical properties (particle size and density) and chemical properties (sulfur content) of tailings on the performance properties of cemented paste backfill. The presented results have shown that the tailings particle size and density has a considerable effect on the properties (strength, cost, water demand, microstructure) of the paste backfill. It was demonstrated that the tailings particle size, particularly the proportions of fines tailings particles (< µm) significantly affect the porosity of the paste backfill and the pore size distribution within it, its water drainage ability and consequently, its strength development and the 9

10 water requirement for a given consistency. It was also shown that not only does the overall porosity influence the strength of the paste backfill, but the pore size distribution plays a decisive role in the strength development of the cemented backfill. The paste backfill water demand increases with the fineness of the tailings material used. Increasing the tailings density is associated with volumetrically higher binder consumption, i.e. more expensive backfill. In general, higher binder consumption gives the paste backfill higher strength. It has been demonstrated that higher sulfur contents in the tailings increases tailings density and consequently give the cemented paste backfill higher strength. This increased strength is caused by a higher binder consumption. However, high sulfur content can lead to strength loss of cemented paste backfill trough sulphate attack. This sulphate comes principally from the oxidation of the sulphide minerals in the non cemented tailings. This work brings new light on the effect of tailings on CPB properties that can contribute to better optimization of paste backfill mixtures and to a better understanding of the behavior of cemented paste backfill. Additionally, these experimental results agree well with those of modeling of the effect of paste backfill components on its properties (Fall and Benzaazoua 3a, Fall and Benzaazoua 3b, Fall and Benzaazoua a). 7 REFERENCES Archibald, J. F., Chew, J. L. and Lausch, P. (199). Use of Ground Waste Glass and Normal Portland Cement Mixtures for Improving Slurry and Paste Backfill Support Performance. 1 th Annual General Meeting of the Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Quebec, May, 1997; (CD-ROM publication) Belem, T., Bussière, B., Benzaazoua, M., 1. The effect of microstructural evolution on the physical properties of paste backfill. Proceedings Tailings and Mine Waste 1, Balkema Rotterdam, ISBN , p. Belem, T., Benzaazoua, M., Bussière, B., Dagenais, A.M.. Effects settlement and drainage on strength development within mine paste backfill. Proceedings Tailings and Mine Waste, Fort Collins, Colorado, Balkema Rotterdam, Balkema : Rotterdam, pp Benzaazoua M. (199). Caractérisation physicochimique et minéralogique de produits miniers sulfurés en vue de la réduction de leur toxicité et de leur valorisation. Thèse de Doctorat de l Institut National Polytechnique de Lorraine Nancy France, 17 Janvier 199. Benzaazoua M., Bussière B., Kongolo M., Mclaughlin J., Marion P., a. Environmental desulphurization of four Canadian mine tailings using froth flotation. International Journal of Mineral Processing : pp Benzaazoua M., Belem, T., Jolette, D., b. Investigation de la stabilité chimique et son impact sur la résistance mécanique des remblais cimentés. Rapport IRSST, IRSST ed., R-: 15p + Annexes. Benzaazoua, M., Fall, M., and Ouellet, S. 3a. Étude pluridisciplinaire visant à mettre au point un outil expert pour la prédiction du comportement des remblais en pâte. Final Report, Contract IRSST no 99-5 (soumis). Benzaazoua, M., Fall, M., Belem, T., 3a. A Contribution to understanding the hardening process of cemented paste backfill. Journal of Minerals Engineering, UK (in press). Bloss, M.,. Below ground disposal (mine backfill). In Paste and Thickened Tailings: A Guide, ed. Jewell, Fourie and Lord, University of western Australia,, pp Brakebusch, F.W., 199. Basics of paste backfill systems, Mining Engineering,, Cook, R.A., Hover, R.C., Mercury porosimetry of hardened cement pastes. Cem. Concr. Res. (1999) Elberling, B., Nicholson, R.V., Reardon, E.J., and Tibble, P. (199). Evaluation of sulphide oxidation rates: laboratory study comparing oxygen fluxes and rates of oxidation product release. Canadian Geotechnical Journal, 31: Elberling, B., Nicholson, R. V. (199). Field determination of sulfide oxidation rates in mine tailings. Water Resources Research, 3 : Fall, M., Benzaazoua, M., 3a. Advances in Predicting Performance Properties and Cost of Paste Backfill. Int. Conf. Tailings & Mine Waste '3, Colorada, USA; A.A. Balkema, 3 Swets & Zeitlinger, Lisse, ISBN , p

11 Fall, M, Benzaazoua, M., 3b. A model for predicting the Performance of underground paste backfill. Proc. Int. Conf. Wast. Tech. & Man. Phil., USA; Ed, J. SWT. & M. pp Fall, M., Benzaazoua, M., 3c. Modeling and Simulation of Paste Backfill Performance Properties. Proceedings of 5 th Canadian Geotechnical Conference; September to October 1, 3 in Winnipeg, Manitoba, Canada, pp Fall, M, Benzaazoua, M., Ouellet a. Experimental characterisation of the influence of mill tailings fineness and density on the quality of cemented paste backfill. International Journal of Minerals Engineering (submitted). Fall, M, Benzaazoua, M. b. Modeling the effect of sulphate on strength development of paste backfill and binder mixture optimization. Journal of Cement and Concrete Research (submitted). Grice, T., 199. Underground Mining with Backfill, nd annual summit, Mine tailings disposal systems. Brisbane, Australian, 199, 1 pp. Hassani, F. and Bois (199). Economic and technical feasibility for backfill design in Quebec underground mines. Final report ½, Canada-Quebec Mineral Development Agreement, Research & Development in Quebec Mines. Contract n. EADM 199, File n.71. Hassani, F., Archibal, J., 199. Mine Backfill, CD- Rom, Canadian Institute of Mine, Metallurgy and Petroleum, 199. Kesimal, A., Ercikdi, B., Yilmaz, E., 3. The effect of desliming by sedimentation on paste backfill performance. Minerals Engineering 1, 3, pp Landriault D., Verburg R., Cincilla W., Welch D., Paste Technology for Underground Backfill and surface tailings disposal applications. Short Course notes Technical Workshop, Vancouver, British Columbia, 11 p. Landriault, D., Paste backfill Mix design for Canadian Underground Hard Rock Mining. 97 th Annual General Meeting of CIM. Rock Mechanics and Strata Control Session. Halifax, Nova Scotia, May 1-1, 1995, pp Landriault D., Verburg R., Cincilla W., Welch D., Paste Technology for Underground Backfill and surface tailings disposal applications. Short Course notes Technical Workshop, Vancouver, British Columbia, 11 p. Leppinen, J.O., Salonsaari, P., Palosaari, V. (1997). Flotation in acid mine drainage control : beneficiation of concentrate. Can. Metall. Q. 3 (), 5-3 Lerche R., Renetzeder H., 19. Development Of Pumped Fill At Grund Mine, Preussag AG Metall, 9th International Conference on The Hydraulic Transport of Solids in Pipes, Rome, Italy, October Kumar, R., Bhattacharjee, B.,. Study of some factors affecting the results in the use of MIP method in concrete. Cem. Concr. Res. 33 () McLaughlin, J., Stuparyk, R., 199. Evaluation of low sulphur rock tailings production at Inco s Clarabelle Mill. In: Turgut, Yalçin (Ed.), Conf. on Innovation in Mineral Processing; Sudbury, Canada. pp Ouellet S., Bussière B., Benzaazoua M., Aubertin M., Fall M., Belem T. (3). Sulphide Reactivity within cemented paste backfill: oxygen consumption test results. Proceedings of the 5 th Annual Canadian Geotechnical Conference and th joint IAH-CNC/CGS Conference, Winnipeg, Manitoba, Canada, September th to October 1 st, 3, pp Stuparyk, R.A., Kipkie, W.B., Kerr, A.N., Blowes, D.W., Production and evaluation of low sulphur tailings at INCO s Clarabelle Mill. Proceedings of Sudbury 95 (Canada), Conference on Mining and the Environment Vol. 1, Vočka, R., Gallé, C., Dubois, M., Lovera, P., Mercury intrusion porosimetry and hierarchical structure of cement pastes. Theory and experiment. Cem. Concr. Res. 3 () Acknowledgments The authors would like to thank the Institut de Recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) and the Fundation of the University of Quebec in Abitibi-Témiscamingue (FUQAT) for financial supporting of this research. We would like also to thank all technicians (particularly Hugues Bordeleau) and chemists of URSTM for undertaking the mechanical and physico-chemical tests. 11