Abstract
Cemented paste backfill (CPB) offers an environmentally sustainable way to utilize mine tailings, one of the largest waste streams in the world. CPB is a support and filler material used in underground mine cavities, which consists of mine tailings, water, and binder material that usually is cement. Replacing cement with secondary raw materials like granulated blast-furnace slag reduces the total CO2 emissions and strengthens the internal microstructure of the CPB. This study characterizes the total- and soluble contents of CPB starting materials and five CPB specimens containing different levels of slag substitution. In addition, phase composition (mineral liberation analysis, MLA) and internal structure (X-ray tomography) of five CPB specimens is documented, and measurements of compressive strength are used to evaluate their suitability as backfill material. Mine tailings and CPB specimens used in this study are rich in sulphates and arsenic, but low in sulphides. Stronger As leaching of ground CPB specimens compared with ground mine tailings is related to the elevating pore water pH during the cement hydration. The hydration product ettringite is found in all CPB specimens and its content is the lowest in the slag containing specimens. X-ray tomography revealed vertically differentiated density structures in the CPB specimens. The lower parts of all specimens are denser in comparison with the upper parts, which is probably due to the compaction of the solid particles at the base. The compressive strength test results indicate that partial substitution of cement with slag improves the strength of the CPB. The total replacement of cement with slag reduces the early strength but gives excellent strength and lower porosity over longer time intervals. The results of the study can be utilized in developing more durable and environmentally responsible CPB recipes for gold mines of similar mineral composition and gold extraction method.
Highlights
The mining of sulphide rich ores may result in an environmental problem called acid mine drainage, Acid mine drainage (AMD)
Minerals 2021, 11, 1068 differences in chemical and phase composition in addition to the internal structure of the Cemented paste backfill (CPB) test pieces were studied to find out how the replacement of cement by slag affects these properties
Methods of characterizing the parent materials, preparing the CPB test pieces, characterizing the test pieces for phase and chemical composition, measuring compressive strength, and performing X-ray tomography investigation are described 2
Summary
Extractive waste is one of the largest waste streams in the world, consisting 26% of all waste in the EU [1]. It consists mainly of waste rocks and mine tailings. The demand for mineral products is predicted to increase by 500% by 2050 [2]. This will dramatically increase the amount of extractive wastes if they are not utilized more effectively. Non-sulphidic extractive wastes are capable of causing contamination of ground and surface waters, in which they release contaminants such as sulphates, metalloids, or metals
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