Utilisation of Water-Washing Pre-Treated Phosphogypsum for Cemented Paste Backfill

Abstract

Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to investigate the feasibility of treated PG (TPG) washed repeatedly using deionised water (DW) for CPB. A water-washing pre-experiment was first conducted to find the proportion with the least DW demand and the effects of water-washing on ordinary PG (OPG). Then, based on the PG:DW ratio obtained from the pre-experiment, the properties of the OPG-based CPB (OCPB) and TPG-based CPB (TCPB) were tested using slump tests, UCS tests, and microstructural analysis. The results show that (1) after 11 water-washings at the PG:DW ratio of 1:1.75, the pH of the supernatant (pH = 6.328) meets the requirements of Chinese standard GB 8978-1996. (2) Water-washing improves the particle gradation quality of PG and removes the soluble impurities adsorbed at the surface of PG crystals. (3) The initial slump values of TCPB are 0.19–1.15 cm higher than that of OCPB, furthermore, the diffusivity values of TCPB are better than the performance of OCPB, with 0.61–1.68 cm of superiority. (4) The UCS values of TCPB are up to 0.838 MPa, 1.953 MPa, and 2.531 MPa, after curing for 7, 14, and 28 days. These are 0.283 MPa, 0.823 MPa, and 0.881 MPa higher than that of OCPB, respectively. It can be concluded that water-washing pre-treatment greatly improves the workability and mechanical property of PG-based CPB. These results are of great value for creating a reliable and environmentally superior alternative for the recycling of PG and for safer mining production.

Fiber-Reinforced Cemented Paste Backfill: The Effect of Fiber on Strength Properties and Estimation of Strength Using Nonlinear Models

“…The cement content played a significant role in enhancing the strength of the CPB. Therefore, in this study, the effects of eight different cement contents (25,20,17,14,13,10, 8 and 7 wt.%) on the UCS of the fiber-reinforced and unreinforced CPB were studied. Some of the data have been published in previous studies [32].…”

“…Therefore, reducing the cement consumption according to different backfill function requirements is an effective method to decrease mine backfilling costs. Besides, certain cement substitutes, such as fly ash and phosphogypsum, have been studied as binders for CPB preparation [15][16][17][18]. However, subject to the production and their inherent harmful factors, these materials can only reduce the cement consumption to a limited extent.…”

Industrial Experiment of Goaf Filling Using the Filling Materials Based on Hemihydrate Phosphogypsum

“…By-product phosphogypsum can be divided into dihydrate phosphogypsum and hemihydrate phosphogypsum according to different production technology of wet process phosphoric acid. Dihydrate phosphogypsum can only be used as aggregate in mine filling [34][35][36]. This method has the problems of high cement consumption and high filling cost.…”

Roof Movement and Failure Behavior When Mining Extra-Thick Coal Seams Using Upward Slicing Longwall-Roadway Cemented Backfill Technology

“…e technical principles of the USLCB are shown in Figure 1 and described as follows [14]. e cemented backfill is prepared in a backfill plant at the surface and is transported underground to stopes through a network of backfilling pipelines [7,[27][28][29]. e extra-thick coal seam is divided into several slices with the deepest slice being mined first and the resulting void being filled with backfill material [30,31].…”