Study on the Preparation and Hydration Properties of a New Cementitious Material for Tailings Discharge

Abstract

Blast furnace slag (BFS) is often used as a cement-based raw material for underground filling and surface cemented paste discharge of tailings during mining processes. This paper studied a new cement-based material (NCM) with BFS to replace ordinary Portland cement (OPC). A uniaxial compressive strength (UCS) experiment was used to test the mechanical strength of samples; X-ray diffraction and thermal gravity experiments were used to test the crystalline phases and amount of hydration products by samples; a scanning electron microscope experiment was used to observe the influence of the hydration products morphology by samples; mercury intrusion porosimetry experiment was used to analyze the pore size distribution of samples. The samples with NCM had an optimum UCS; the crystalline phases of the hydration products were similar in OPC and NCM. However, the amount of product formed in OPC was less than that in NCM at the same curing time; more ettringite and calcium silicate hydrate were produced in samples with NCM, which filled the pores and enhanced the UCS of the samples. The final mercury intrusion volume of the samples with NCM were lower than the samples with OPC at the same curing time, which showed that samples with NCM had lower porosities. For the samples with NCM and OPC cured from 7 days to 28 days, the mercury intrusion volume was reduced by 18% and 13%, and the most common pore size of the samples reduced by 53% and 29%, respectively. This showed after 21 days curing time, the pores of all the samples getting smaller; however, the samples with NCM were more compact. The main ingredients of the NCM were clinker, lime, gypsum and BFS, and its ratio was 14:6:10:70. The content of additives to NCM was 0.4%, and the ratio of sodium sulfate: alum: sodium fluorosilicate was 2:1:1.Processes 2019, 7, 47 2 of 17 combined both methods and proposed the technology of cemented paste discharge of tailings (CPDT) [10,11]. The method involved adding some cement to the tailings and discharging them to valleys or subsidence areas; the tailings need to be transported by pipes or belts. This method guarantees the stability of the tailings for the cemented piles. In addition, mines no longer need to build tailings pond and can also achieve safe pile-up. Because the cemented tailings pile can be built up to a high height, the limited footprint can pile up more tailings than tailings ponds. Presently, this technology has been applied and developed in some metal mines [11].During the cemented paste backfill, the amount of cement was 2% to 7% of the total weight of the tailing slurry, and it may be up to 10% to remain independent across pillar extraction process [12]. Cement costs account for more than 60-80% of the filling costs, as discussed by Li et al. [13]. The idea of CPDT was derived from cemented paste backfill, thus, the process of CPDT was similar to this, and the cost of cement also occupied a large proportion of CPDT costs. Therefore, the search for cheap, cementitious industrial by-products to replace cement and ...

Study on Relationship between UCS of Cemented Tailings Backfill and Weight Losses of Hydration Products

“…Previous works have been studied the phase composition of the OPC hydration products [16,22,28,29]. e erefore, XRD analysis is not carried out for samples of the OPC-CTB and OPC paste.…”

“…TG/DTG experiments were performed on prepared OPC-CTB samples to test the weight losses of the hydration products. For OPC paste, a scholar conducted a thermal analyses experiment and found that its hydration products include C-S-H, Ca(OH) 2 , and CaCO 3 [16]. erefore, the TG/DTG curve of OPC paste is not listed in this paper.…”

“…In the first stage, the peak temperature of weight loss is 128.51°C, and the weight loss is 1.90%, corresponding to the dehydration reactions of the C-S-H. In the second stage, the peak temperature of weight loss is 422.34°C, and the weight loss is 0.44%, attributing to the de-hydroxylation of Ca(OH) 2 [16,32,33,35]. In the third stage, the peak temperature of weight loss is 689.10°C, and the weight loss is 1.86%, corresponding to the thermal decomposition of CaCO 3 .…”

“…It indicated that the weight loss of the NCM sample at 110∼200°C is more than OPC. And it is believed that more cement-based hydration products were generated in the NCM, so the stress of the NCM sample is higher [16]. Ding quantitatively analyzed the hydration products of concrete materials by means of thermal analyses [17].…”

Recent Advances in Fluid Flow in Fractured Porous Media

“…Hou, Y. et al, Study on the Preparation and Hydration Properties of a New Cementitious Material for Tailings Discharge[64].…”