A study on the effects of cement-based material grouting on water quality in loose, water-bearing sandy layers and the mechanisms of pollutant degradation based on laboratory experiments

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Abstract
The grouting operations have the potential risk of causing pollution to the environment during the mine management process. The large volume of slurry may have an impact on groundwater quality and even lead to groundwater pollution. Given this, it is of vital significance to carry out research on the pattern and mechanism of the impact of typical grouting materials on regional groundwater quality, in order to assess the degree of grouting pollution, and the degradation cycle, as well as to attenuate, prevent and control the adverse impacts brought about by it. Based on the hydrogeological conditions of the study area, a dynamic seepage reaction system was established. Constant flow long-term percolation tests were conducted for three groups: a control group without grout (W), a cement-grouted (C), and a (cement-sodium silicate)-grouted (CS). Comprehensive water quality analyses were performed on the corresponding leachate samples. The study found: (1) In the later stages of the experiment, white flocculent precipitates were observed in the cement-grouted leachate (C group), while the leachate from the cement-sodium silicate grouted (CS group) initially appeared yellow. (2) In the C group, the leachate led to the formation of Ca(OH)2 (CH) crystals on the surface of the sand grains, whereas the leachate in the CS group altered the surface morphology of the sand grains. (3) After grouting, the initial leachate exhibited high concentrations of most ions. However, as infiltration progressed, the concentrations of these ions decreased significantly. Additionally, the concentration trend of some ions in the grouted leachate samples has a differentiated pattern. (4) After grouting, the leachate was slightly alkaline, with elevated total hardness and total dissolved solids, and exhibited reducing properties. The hydrochemical structure underwent significant changes. (5) Different patterns of pollution degradation due to the ring-band structure of the grouting stone body. (6) The ionic concentrations in the leachate exhibit a trend of attenuation or rebound under seepage action, generally showing a dynamic recovery towards the control group concentrations. The degradation trends of the main pollutants for both types of grout largely conform to an exponential decay model.

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