Cemented paste backfill for mineral tailings management: Review and future perspectives

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Foundations of engineering geology

Preparation and microstructure of fly ash geopolymer paste backfill material

Effect of mineral admixtures on flow properties of fresh cemented paste backfill: Assessment of time dependency and thixotropy

The pumping ability and placement performance of fresh cemented paste backfill (CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement (PC), a newly released commercially manufactured cement called Minecem (MC) and fly ash (FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature (25 °C), with regards to the unconfined compressive strength (UCS) performance, the replacement of 4% PC mixed CPB (28 days UCS 425 kPa) to 3% MC mixed CPB (28 days UCS 519 kPa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water (MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.

Effects of water content, water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

Cemented paste backfill (CPB) is primarily used for backfilling underground voids at George Fisher Mine (Mount Isa, Australia). The objective of this paper is to summarise the geotechnical characterisation of the tailings and the rheological properties of the CPB as determined from a laboratory testing program undertaken at James Cook University. Two binders were examined [a General Purpose cement and a slag blend cement] over a range of dosages from 0 to 6% and CPB mix solids content in the range of 72–78%. The slump tests were carried out using the standard cone (ASTM C 143) used for concrete and a cylinder with 110 mm (diameter) × 110 mm (height), whereas the yield stress was measured using a shear vane (Brookfield vane spindle V-73). The index characteristics of the tailings including the grain size distribution, liquid limit, plastic limit, specific gravity were determined as per ASTM standards. This paper will then discuss the interrelationships among the solid content, slump, saturated density and the yield stress of the CPB. It is shown that there is strong correlation between the two different slump test devices used in this study. The smaller cylindrical device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test. There is also strong inter-relationship among solid content, slump, yield stress, and bulk density. Increasing the solid content increases the bulk density and yield stress, but reduces the slump. While there is hardly any difference between the two binder types used in this study in terms of flow parameters, namely the yield stress and slump, the binder dosage has an effect. At any specific solid content, higher binder dosages lead to a drop in the slump and increase in the yield stress. The difference is more pronounced in dense slurries. It is also strongly believed that the trends and relationships developed in this study may be valuable for the other mining operations using CPB.

Flow Characteristics of Cemented Paste Backfill

Cemented paste backfills (CPBs) are widely used in backfilling underground mine voids. They are fine-grained mine tailings with significant clay content, with a small dosage of a general pu...

Laboratory Study on Strength Development in Cemented Paste Backfills

This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Mining is one of the major economic activities in Australia, which produces millions of tonnes of waste materials every year. Mine tailings derived from crushed waste rock are generally utilized as backfilling material to fill the underground voids created during mining operations. Generally, additives are used to enhance the engineering behaviour of soils and concrete. Cement is one of the most popular additives used to improve the properties of soils. Lately, there have been attempts to use pozzolanic materials such as fly ash and slag to partially replace cement. Excessive cement usage in soil may be reduced by using supplementary cementitious materials such as fly ash and slag, blended cement and geopolymers in some geotechnical applications, which should lead to environment sustainability and substantial cost savings. This paper summarizes the effectiveness of three type of binder in paste fill in terms of their strength and stiffness.

Effects of Different Binders on the Strength and Stiffness of Paste Fills

Mining and dredging are two major economic activities in Australia, and millions of tonnes of waste materials are produced every year by these activities. Mine tailings derived from crushed waste rock, and dredged mud removed from waterways during maintenance dredging, require effective means of disposal. While mine tailings are generally utilized as backfilling material to fill the underground voids created during mining operations, dredged mud is commonly used in land reclamation. In underground mining, accidents have resulted in severe economic damage and loss of lives, while in land reclamation, because of the very slow sedimentation and consolidation processes, future infrastructure development can be delayed. This paper summarizes an extensive literature review on the use of geopolymers and pozzolanic materials in stabilizing geomaterials. Generally, additives are used to enhance the engineering behaviour of soils and concrete. Cement is one of the most popular additives used to improve the properties of soils. Lately, there have been attempts to use pozzolanic materials such as fly ash and slag to partially replace cement. Excessive cement usage in soil may be reduced by using supplementary cementitious materials such as fly ash and slag, blended cement and geopolymers in some geotechnical applications, which should lead to environment sustainability and substantial cost savings.

Naguleswaran Niroshan

Papers

Flow Characteristics of Cemented Paste Backfill

Laboratory Study on Strength Development in Cemented Paste Backfills

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Effects of Different Binders on the Strength and Stiffness of Paste Fills

A review on use of pozzolanic materials and geopolymers in stabilizing mine tailings and dredged mud