A New Application of Solvent Extraction to Separate Copper from Extreme Acid Mine Drainage Producing Solutions for Electrochemical and Biological Recovery Processes

Over the last decade, AMD waters have gained more attention as a potential source of metals due to the emerging need to recover or recycle metals from secondary resources. Metals recovery supports sustainability and the development of a circular economy with benefits for resource conservation and the environment. In this study, five extractants (Acorga M5640, LIX 54, LIX 622, LIX 622 N, and LIX 864) diluted (15% (v/v)) in Shell GTL with 2.5% (v/v) octanol were compared and evaluated for Cu recovery from an extreme AMD sample (5.3?±?0.3 g/L Cu) collected at the inactive São Domingos Mine in the Iberian Pyrite Belt of Portugal. Of the five extractants, Acorga M5640 showed the best selective efficiency. Further tests showed that 30% (v/v) of this extractant was able to selectively extract ≈ 96.0% of the Cu from the AMD in one extraction step and all of the remaining Cu (to below detection) in three steps. Among the different stripping agents tested, 2 M sulfuric acid was the most efficient, with ≈ 99% of the Cu stripped, and the recyclability of the organic phase was confirmed in five successive cycles of extraction and stripping. Furthermore, contact time tests revealed that the extraction kinetics allows the transfer of ≈ 97% of the Cu in 15 min, and aqueous to organic phase ratios tests demonstrated a maximum loading capacity of ≈ 16 g/L Cu in the organic phase. Raising the concentration of Cu in the stripping solution (2 M sulfuric acid) to ≈ 46 g/L through successive striping steps showed the potential to recover elemental Cu using traditional electrowinning. Finally, a biological approach for Cu recovery from the stripping solution was evaluated by adding the supernatant of a sulfate-reducing bacteria culture to make different molar ratios of biogenic sulfide to copper; ratios over 1.75 resulted in precipitation of more than 95% of the Cu as covellite nanoparticles.

Graphical Abstract

     

Effects of random heterogeneity of soil properties on bearing capacity

This study examines the effect of random heterogeneity of soil properties on bearing capacity. The stochastic soil property considered is the undrained shear strength and two major sources of uncertainty are identified with it: inherent spatial variability (modeled as a non-Gaussian, homogeneous stochastic field) and uncertainty in the estimation of its expected value (modeled as a random variable). The two sources of uncertainty are treated separately, before being eventually combined. A Monte Carlo simulation approach is followed in combination with non-linear finite element analysis. It is demonstrated that the inherent spatial variability of soil shear strength can drastically modify the basic form of the failure mechanism in this bearing capacity problem. Consequently, there is no ‘average’ failure mechanism (surface) in this problem, leading to the conclusion that Monte Carlo simulation is the only methodology capable of providing a solution to this geomechanics problem. It is further demonstrated that this behavior of the failure mechanism translates into a substantial reduction in the ultimate bearing capacity (in an average sense), compared to the corresponding deterministic (homogeneous soil) case. In addition, differential settlements are computed in the stochastic analysis, something impossible in a deterministic analysis of a symmetric problem. A parametric study is performed using fragility curves to investigate the effects of various probabilistic parameters involved in the problem. It is found that the coefficient of variation and the marginal probability distribution of the soil's shear strength (both controlling the amount of loose pockets in the soil mass) are the two most important parameters in reducing the bearing capacity (in an average sense) and producing substantial differential settlements in heterogeneous soils (compared to homogeneous soils). A technique is finally introduced for determining ‘overall’ fragility curves that account for both inherent soil spatial variability and uncertainty in the expected value of soil strength. Based on such ‘overall’ fragility curves obtained at failure (ultimate bearing capacity), nominal values of the bearing capacity of a heterogeneous soil deposit corresponding to an exceedance probability of 5% are established for a range of probabilistic characteristics.     

Correction to: A New Application of Solvent Extraction to Separate Copper from Extreme Acid Mine Drainage Producing Solutions for Electrochemical and Biological Recovery Processes

Mine Water and the Environment -     

Buried Pipelines Subject to Subgouge Deformations

Engineers often model pipe/soil interaction events based on the concept of subgrade reactions originally proposed by Winkler. Engineering models often utilize beam and nonlinear/plastic spring elements to represent pipelines and the surrounding soil medium, respectively. The spring formulations, defining soil resistance to deformations in three-dimensional space, are usually assumed to be independent and the responses are discrete between adjacent soil zones. However, this idealization does not truly replicate a soil medium behavior. This study presents coupled numerical analyses of pipeline for the specific problem of subgouge deformations due to ice gouge events. Three dimensional continuum analyses of coupled pipe/soil/ice keel interaction using an explicit arbitrary Lagrangian finite- element approach were performed. The study compares the continuum finite-element results with Winkler-type analysis for the specific analyzed problem. A Lagrangian adaptive meshing technique was employed to model very large movement and achieves a steady-state condition; and reasonable ice/soil and soil/pipe interaction interfaces are employed. The numerical analysis shows the potential for continuum modeling of pipe/soil interaction events and develops a better understanding of ice gouging and pipe/soil/ice keel interaction.