Prediction of neutral mine drainage (NMD) chemistry is difficult with the predictive tools developed for acid mine drainage (AMD). To address this problem, a methodology to assess NMD risk was developed using Lac Tio Mine waste rock as a positive control. The methodology compares the maximum potential for contaminant release (in this case, nickel) using the waste rock’s total metal content and the sorption capacity of the material (qmax) combined with a mineralogical assessment and modified kinetic leaching experiments that use a chelating agent to prevent immobilization processes from occurring. The results indicate that the potential NMD risk associated with Lac Tio waste rock would be assessed as probable with the proposed methodology. Indeed, the total nickel concentrations in the Lac Tio waste rock range from 270 to 590 mg/kg. The nickel is found in Ni-rich pyrites, which proved to effectively leach when no immobilization occurred (using ethylenediaminetetraacetic acid, or EDTA, leaching). The material’s sorption capacities were between 127 and 197 mg/kg of Ni. The sorption capacity to total Ni content ratio of the material was < 1, indicating that the material has fewer sorption sites for Ni than Ni contained within the material, thereby underscoring the potential risk of Ni leaching over time. The approach proposed in this work provides an additional tool for the assessment water quality risk associated with NMD.

In Jiaozuo mining area of North China coal field, there are multiple strong water-richness aquifers close to the coal seam. In order to prevent floor water inrush accident, it is need to be reinforced by floor grouting before mining. According to the changes of the mechanics and hydrogeological properties of the floor key rock strata after floor grouting, the coal seam floor is divided into 'two zones' of 'water conduction fracture zone' and 'mechanical strength damage zone'. The composite water control model of 'floor structure stability water control key layer' and 'floor damage infiltration water control key layer' is established after grouting reinforcement of upper hard rock aquifer. Microseismic(MS) technology is used to analyse the characteristics of 'two zones' and the water control capability of 'dual key layers' in fault regions and no-fault regions respectively of experimental working face. It is revealed that the L8 limestone plays the role of mechanical barrier key layer after grouting. The change of elastic modulus of rock mass before and after grouting is measured by borehole ultrasonic method, which result shows that the elastic modulus of different rock mass increases by 40% to 852% respectively after grouting. By using the formula method, FLAC3D numerical simulation and field measurement, it is found that the failure depth of the floor after grouting is reduced by 51% compared with that without grouting. Seven influencing factors for floor water control 'dual key layer' are proposed, which are quantified by AHP (Analytic Hierarchy Process) method. A scheme of 'dual key layer' water control capability evaluation is formed by AHP method and influencing factors evaluation method. It is revealed that fault activation and fault with water-filling are the main factors that affect the failure of water control capability of 'dual key layer' and floor water inrush. The results of the research are consistent with the water inrush of the experimental working face, which will contribute to the early warning, prevention and evaluation of floor water inrush in mines with the same hydrogeological conditions.

The chemical composition of mine water discharged from flooded underground mines typically improves over time. This phenomenon is called first flush and can be described by a characteristic curve. Shortly after the mine water begins to discharge, water constituent concentrations rise and then fall in an almost exponential curve, improving water quality over time. In this study, the change in mine water quality was investigated throughout the mine water body. This mine water body commonly consists of different water bodies with individual densities, resulting in mine water stratification. Anthropogenic disturbance of the mine water body can disrupt this stratification and also the positive effect of the first flush. To better understand and predict the first flush, the first flush was simulated experimentally using an analogue model of a flooded underground mine, the Agricola Model Mine. The results were compared with field studies to help understanding and predicting the change in mine water quality. Overall, the results suggest that the first flush occurs throughout the mine water body, making it similar to a chemical reactor. This better understanding of the process can lead to more effective mine water management and design of mine water treatment facilities.Graphical