Bayram Ercikdi

The effect of desliming by sedimentation on paste backfill performance

Abstract One of the most important characteristics of a backfill material is the particle size distribution. In this paper, the authors have focused the effect of deslimed mill tailings on paste backfill performance at a copper–zinc mine in northeast Turkey. The use of sedimentation methods to deslime has a widespread utilisation and regarded as a true fractional size analysis practice. The common laboratory method of beaker decantation was used for desliming in order to determine the optimum particle size distribution. For studying the beaker decantation, two mine tailings, namely tailings samples A and B are used which have particles 52 and 54 wt.% finer than 20 μm, respectively. The fines content (−20 μm) of each tailing were reduced to 15, 20, 25 and 30 wt.% via desliming. Deslimed tailings then were tested to investigate the relationship between particle size and strength gain. It was found that strength ranges of the deslimed tailings were from 12% to 52% higher than as-received mill tailings.

Utilization of industrial waste products as pozzolanic material in cemented paste backfill of high sulphide mill tailings.

In this study, the potential use of the industrial waste products including waste glass (WG), fly ash (FA), granulated blast furnace slag (GBFS) and silica fume (SF) as pozzolanic additive for the partial replacement of ordinary Portland cement (OPC) in cemented paste backfill (CPB) of sulphide-rich mill tailings was investigated. The influence of these industrial waste products on the short- and long-term mechanical performance of CPB was demonstrated. The rate of development of strength of CPB samples tended to slow down when the pozzolanic wastes were incorporated or increased in dosage in the binder phase. Severe losses (by 26%) in the strength of CPB samples produced from exclusively OPC occurred after an initial curing period of 56 days. The addition of WG (10-30 wt%) as a partial replacement of OPC was observed to aggravate further the strength losses of CPB samples. GBFS, FA and SF appeared to improve the long-term performance of CPB samples; albeit, only GBFS and SF could be incorporated into the binder phase only at certain levels i.e. up to 20 wt% GBFS and 15wt% SF in order to maintain a threshold strength level of 0.7MPa over 360 days. SEM studies have provided further insight into the microstucture of CPB and confirmed the formation of deleterious gypsum as the expansive phase. These findings have demonstrated that the industrial waste products including GBFS and SF can be suitably used as mineral additives to improve the long-term mechanical performance of CPB produced from sulphide-rich tailings as well as to reduce the binder costs in a CPB plant.

Assessment of strength properties of cemented paste backfill by ultrasonic pulse velocity test

Ultrasonic pulse velocity (UPV) test is one of the most popular non-destructive techniques used in the assessment of the mechanical properties of concrete or rock materials. In this study, the effects of binder type/dosage, water to cement ratio (w/c) and fines content (<20 μm) of the tailings on ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) samples were investigated and correlated with the corresponding unconfined compressive strength (UCS) data. A total of 96 CPB samples prepared at different mixture properties were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UPV and UCS of CPB samples of ordinary Portland cement (CEM I 42.5 R) and sulphate resistant cement (SRC 32.5) initially increased rapidly, but, slowed down after 14 days. However, UPV and UCS of CPB samples of the blast furnace slag cement (CEM III/A 42.5 N) steadily increased between 7 and 56 days. Increasing binder dosage or reducing w/c ratio and fines content (<20 μm) increased the UCS and UPV of CPB samples. UPV was found to be particularly sensitive to fines content. UCS data were correlated with the corresponding UPV data. A linear relation appeared to exist between the UCS and UPV of CPB samples. These findings have demonstrated that the UPV test can be reliably used for the estimation of the strength of CPB samples.

Effect of natural pozzolans as mineral admixture on the performance of cemented-paste backfill of sulphide-rich tailings

This paper presents the effect of the natural pozzolans as mineral additives on the short- and long-term strength and stability performance of cemented paste backfill (CPB) samples. Prior to their use in CPB studies, the natural pozzolans — the volcanic tuffs (Akkus Trass [AT] and Fatsa Trass [FT]) and pumice (KP) — were tested for their pozzolanic characteristics. These tests revealed that the pozzolanic activity of the natural pozzolans is closely inter-related with their content of reactive silica and, accordingly, KP has the highest pozzolanic activity. The addition, or increasing the amount, of natural pozzolans in the binder phase resulted in a slower rate of strength development of CPB samples. The deterioration in stability of CPB samples prepared from Portland cement (PC) alone (i.e. a strength loss of 24.6%) occurred following 56 days. The replacement of PC with FT and AT led to even higher losses in strength. However, the addition of KP (up to 30 wt%) mitigated, to a certain extent, long-term strength and stability problems with the losses in strength of CPB samples consistently lower than 20%. It can be inferred that the performance of the natural pozzolans as a mineral additive in CPB is dependent intimately on their pozzolanic characteristics.

Strength and ultrasonic properties of cemented paste backfill.

This paper presents the strength (UCS) and ultrasonic pulse velocity (UPV) properties of cemented paste backfill (CPB) produced from two different mill tailings (Tailings T1 and T2). A total of 240 CPB samples with diameter×height of 5 × 10 cm and 10 × 20 cm prepared at different binder dosages (5-7 wt.%) and water-to-cement ratios (3.97-5.10) were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UCS and UPV of CPB samples increased with increasing the binder dosage and reducing the w/c ratio irrespective of the sample size and tailings type. CPB samples with a diameter × height of 5 × 10 cm were observed to produce consistently higher (up to 1.69-fold) UCSs than those of 10 × 20 cm CPB samples at all binder dosages and w/c ratios. However, at the corresponding binder dosages and w/c ratios, the maximum variation of UPV between the CPB samples of 5 × 10 cm and 10 × 20 cm was only 7.45%. Using the method of least squares regression, the UCS values were correlated with the UPV values for CPB samples of 10 × 20 cm in size. A linear relation with a high correlation coefficient appeared to exist between the UCS and UPV for CPB samples. These findings suggest that the UPV is essentially independent of the sample size. In this regard, the UPV test can be suitably exploited for the rapid estimation of the strength and quality of CPB samples even using small samples with concomitant benefits of reducing sample size.

Predicting the uniaxial compressive strength of cemented paste backfill from ultrasonic pulse velocity test

Abstract The aim of this study is to investigate the predictability of the uniaxial compressive strength (UCS) of cemented paste backfill (CPB) prepared from three different tailings (Tailings T1, Tailings T2 and Tailings T3) using ultrasonic pulse velocity (UPV) test. For this purpose, 180 CPB samples with diameter × height of 5 × 10 cm (similar to NX size) prepared at different binder dosages and consistencies were subjected to the UPV and UCS tests at 7–56 days of curing periods. The effects of binder dosage and consistency on the UPV and UCS properties of CPB samples were investigated and UCS values were correlated with the corresponding UPV data. Microstructural analyses were also performed on CPB samples in order to understand the effect of microstructure (i.e. total porosity) on the UPV data. The UPV and UCSs of CPB samples increased with increasing binder dosage and reducing the consistency irrespective of the tailings type and curing periods. Changes in the mixture properties observed to have a lesser extent on the UPV properties of CPB, while, their effect on the UCS of CPB was significant. Empirical equations were produced for each mixture in order to predict the UCSs of CPB through UPV. The validity of the equations was also checked by t- and F-test. The results showed that a linear relation appeared to exist between the UPV and UCS with high correlation coefficients (r ≥ 0.79) and all models were valid by statistical analysis. Mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses have revealed that the UPV properties of CPB samples were highly associated with their respective microstructural properties (i.e. total porosity). The major output of this study is that UPV test can be effectively used for a preliminary prediction of the strength of CPB.

Core size effect on the dry and saturated ultrasonic pulse velocity of limestone samples.

This study presents the effect of core length on the saturated (UPVsat) and dry (UPVdry) P-wave velocities of four different biomicritic limestone samples, namely light grey (BL-LG), dark grey (BL-DG), reddish (BL-R) and yellow (BL-Y), using core samples having different lengths (25-125mm) at a constant diameter (54.7mm). The saturated P-wave velocity (UPVsat) of all core samples generally decreased with increasing the sample length. However, the dry P-wave velocity (UPVdry) of samples obtained from BL-LG and BL-Y limestones increased with increasing the sample length. In contrast to the literature, the dry P-wave velocity (UPVdry) values of core samples having a length of 75, 100 and 125mm were consistently higher (2.8-46.2%) than those of saturated (UPVsat). Chemical and mineralogical analyses have shown that the P wave velocity is very sensitive to the calcite and clay minerals potentially leading to the weakening/disintegration of rock samples in the presence of water. Severe fluctuations in UPV values were observed to occur between 25 and 75mm sample lengths, thereafter, a trend of stabilization was observed. The maximum variation of UPV values between the sample length of 75mm and 125mm was only 7.3%. Therefore, the threshold core sample length was interpreted as 75mm for UPV measurement in biomicritic limestone samples used in this study.

Practical Importance of Tailings for Cemented Paste Backfill

Mineral processing methods, such as flotation, are used to treat low-grade ores from mining operations; however, a significant amount of tailings are then generated (typically 95–98% of the feed ore). Therefore, mineral processing must also be essentially regarded as a “waste/tailings management” project (Ercikdi et al. 2012). The disposal, stability and safety of tailings, and their effects on water and soil, are important technical and environmental problems. For example, sulphide (i.e. pyritic) tailings can lead to the generation of acid mine drainage (AMD) when they are disposed under atmospheric conditions. This results in the release/mobility of heavy metals, such as arsenic (As), copper (Cu) and zinc (Zn) with the concomitant pollution of water resources and soil (Fig. 2.1).

Utilisation of construction and demolition waste as cemented paste backfill material for underground mine openings

This study presents the utilisation of finely ground construction and demolition waste (CDW) as partial replacement (5-15 wt.%) to sulphide tailings on the short- and long-term strength, durability (i.e. no loss of strength) and microstructural properties of cemented paste backfill (CPB) over a curing period of 360 days. The CPB samples containing CDW were prepared at binder dosages of 7.5 and 8.5 wt.%, while control samples (full tailings) were only produced at 8.5 wt.% binder dosage. A total of 108 CPB samples were subjected to the unconfined compressive strength (UCS), acid/sulphate (pH, SO42-) and microstructure (MIP, XRD etc.) tests. Despite its limited contribution to the resistance of CPB to acid and sulphate attack, the use of CDW as partial replacement (5-15 wt.%) to sulphide tailings enhanced the strength properties of CPB samples by decreasing the total and macro porosity. The UCSs and pH values of CPB samples increased with increasing the CDW content in CPB mixtures, while the generation of sulphate ions (SO42-) decreased irrespective of the binder dosages. Compared with control samples prepared at 8.5 wt.% binder dosage, 5.3-19.5% higher UCS values were obtained for the CPB samples containing 15 wt.% CDW prepared even at 7.5 wt.% binder dosage. Mercury intrusion porosimetry (MIP) analyses proved the beneficial effect of the use of CDW on the microstructural properties (i.e. total porosity) of CPB. These findings suggest that CDW materials can be suitably used as backfill material in the mining industry to fill underground voids created during the ore production. This offers safe disposal and hence environmentally sound management of CDW.

Yüksek Fırın Cürufu ve Perlit İkamesinin Çimentolu Macun Dolgunun Mekanik ve Mikroyapı Özelliklerine Etkisi

Son yillarda Portland cimentosu (PC) yerine belirli oranlarda dogal ve yapay puzolanlarin kullanilmasi, cimentolu macun dolgunun (CPB) dayanim ve durayliliginin iyilestirilmesi, asit ve sulfat etkisine karsi direncinin arttirilmasi ve baglayici maliyetlerinin azaltilmasi icin oldukca yaygin hale gelmistir. Bu calismada yuksek firin curufu (YFC) ve perlit (P) ikamesinin CPB’nin mekanik ve mikroyapi ozelliklerine etkisi arastirilmistir. PC yerine agirlikca %20 YFC ve P ikame edilerek hazirlanan 84 adet CPB numunesi 7, 14, 28 ve 56 gunluk kur sureleri sonunda tek eksenli basinc dayanimi ve gozeneklilik (porozite) testlerine tabi tutulmustur. YFC’li numuneler 7-14 gunde PC numunelerine gore daha dusuk dayanim uretirken 28-56 gunde bu numunelerin basinc dayanimini gecmistir. Gozeneklilik sonuclari incelendiginde, YFC’li numunelerin gozenekliligi kur suresinin artmasiyla daha fazla iyilesme gostermistir. Perlit katkili numuneler ise basinc dayanimi ve gozeneklilik gelisimi acisindan zayif kalmistir. Elde edilen bulgular YFC’nin CPB icerisinde belirli oranlarda kullaniminin mekanik ve mikroyapi ozellikleri acisindan faydali oldugunu gostermistir.