MINING CHEMICALS in underground mine backfill. Due to the progressive global shift towards underground mining, mine backfill( MBF) practices are becoming a frequent must in flowsheets. MBF reduces the amount of tailings stored on surface by placing them underground together with water and cement, with the aim to fill the voids. This procedure also allows miners to extract material nearby without compromising global stability( avoiding other issues such as subsidence).
To achieve this goal, the hardened paste must comply with strict strength requirements which are normally achieved by increasing the amount of cement in the mix. In the race to net zero many mines have signed strict environmental policies, which compromise the cost balance of any process using cement, including MBF. Sika says this compels the businesses to utilise chemicals that reduce the amount of binder, and therefore the carbon footprint, while improving the performance of the mix at all stages.
MBF consists of reintroducing mine tailings combined with cement and water back into the mined voids via gravity or pumping. This practice is performed with the objective to fill the void left by mining to promote global stability to the mine to allow further underground mining activities to take place. Thus, reaching the desired strength after curing is critical to maintain the mining schedule.
High proportions of water in the mix design have a negative impact on the strength of the cured paste. Water, however, improves the rheological properties of the paste, enhancing the mixture’ s fluidity, and lowering the required pressure head to distribute paste into the stopes. The use of Sika ® admixtures therefore helps to improve the rheological properties of the paste by decreasing the water input and increasing the strength of the mix without the addition of extra cement.
The ideal Sika solution depends on the mineralogical composition of the tailings, which is unique for each mine. In addition, the admixture behaviour must be flexible,
The use of Sika ® admixtures in mine backfill therefore helps to improve the rheological properties of the paste by decreasing the water input and increasing the strength of the mix without the addition of extra cement
The Sika ® multinational brand provides tailor-made reliable and sustainable chemical solutions to many industries, including the mining business. The application of Sika technologies and know-how it says supports more sustainable procedures and greener( and more profitable) practices.
The presentation stated:“ Each mine has different mineralogy, which makes every project unique. Finding the right cement and admixture can therefore be a time-consuming task, which directly affects the profitability of the mine, especially during field testing manoeuvres. As such, the development of tools and techniques which shorten the time between testing and decision-making are crucial to resume exploitation fast.” to compensate for the compositional heterogeneity of the tailings, offering the highest performance possible. Sika solutions are customised in the laboratory for each case, however, industrial tests are key to optimise the cost / benefit balance of the mine.
The presentation focused on a real world example. Sika Ecuatoriana SA has conducted numerous laboratory tests on samples of an underground gold tailings, identifying the best fitting admixture for the current needs of the mine. Industrial tests have been carried out at the mine, to prepare the paste plant to include this extra component in the flow chart, and to adjust the admixture dosage. Three-dimensional( 3D) plots were used as a tool to assess the effectiveness of Sika admixtures in paste with changing cement percentages.
The paper said that the use of Sika admixtures increases the solids ratio and decreases the amount of water, improving the strength at all ages. The average strengths in samples with 12 % cement without admixtures are comparable to the strengths obtained in samples with Sika admixture with cement contents of 9 %. The trends also reflect similar strengths in samples without admixture using 9 % cement and samples with Sika admixture with < 6 % cement. This fact indicates that 25 % of cement can be saved due to the use of the Sika Stabilizer- 301 MBF EC.
Given that the mine places 1 Mt of paste underground annually and typically consumes around 96,000 t of cement, this translates to a saving of 24,000 t of cement. From a sustainability standpoint, this saving yields two primary advantages: first, a comparison between the carbon footprint of producing 1,800 t of the admixture versus that of 24,000 t of cement; and second, the impact on transportation. Specifically, there is a 92.5 % decrease in the mass required to be transported to the mine, highlighting significant environmental and logistical benefits.
The comparison of the trends at 3, 7 and 28 days showed that the trend lines of the strengths with and without Sika admixture gradually drift apart. This is caused by the use of Sika admixture which further increases the strengths over time. This fact is also observed in experiments where the cement content is kept constant. Strength trends of samples with 2 and 3 % admixture dosages, although yielding very different initial strengths( 3 and 7 days) overlap after 28 days. This stark difference might be useful to adapt paste designs in plugs, where higher initial strengths are required
Industry tests indicate that Sika Stabilizer- 301 MBF EC admixture improves the workability of the mix design and increases the strength of the paste once hardened. Operational benefits include lower head pressure; reduction of slurry lumps; constant flow rate; instant fluidisation of the slurry; increase in the ratio of solids in the slurry; plus less water needed for the mix.
Benefits in hardened state include increased strengths at all ages; reduction of 25 % of cement required to achieve given strengths; and reduction of the carbon footprint.
The paper concludes:“ The tailormade solution Sika Stabilizer-301 MBF EC reduces the amount of cement required to achieve the required strength in the UG gold mine MBF operations. Sika admixtures are therefore not only economically advantageous for the client but are also a sustainable solution.”
International Mining | MAY 2025 59