Diagnosis and Optimization of Gold Ore Flotation Circuit via Linear Circuit Analysis and Mass Balance Simulation

The aim of this study is to diagnose and optimize a closed multistage gold ore flotation circuit in an operational industrial plant. Linear circuit analysis (LCA), a partition-based model, and a mass balance model using flotation first-order kinetics are employed to diagnose the current process. The result shows that the current circuit operates with high recovery but the gold grade of the final concentrate is low owing to the low buoyancy ratio. Hence, several alternative circuits with different streamlines and cell arrangements are proposed and simulated using LCA and a mass balance model. The result suggests that if the current process is changed to an alternative circuit in which the floated product stream of the rougher bank is changed, then the gold grade of the concentrate can be improved by 128%. Finally, the current circuit is optimized by changing it to an alternative circuit. This study provides a methodology for adapting the simulation of optimization for the flotation circuit of an industrial plant via LCA and mass balance simulation.

Quantifying floodwater impacts on a lake water budget via volume-dependent transient stable isotope mass balance

Isotope mass balance models have undergone significant developments in the last decade, demonstrating their utility for assessing the spatial and temporal variability in hydrological processes and revealing significant value for baseline assessment in remote and/or flood-affected settings where direct measurement of surface water fluxes to lakes (i.e. stream gauging) are difficult to perform. In this study, we demonstrate that isotopic mass balance modelling can be used to provide evidence of the relative importance of direct floodwater inputs and temporary subsurface storage of floodwater at ungauged lake systems. A volume-dependent transient isotopic mass balance model was developed for an artificial lake (named lake A) in southern Quebec (Canada). This lake typically receives substantial floodwater inputs during the spring freshet period as an ephemeral hydraulic connection with a 150 000 km2 large watershed is established. First-order water flux estimates to lake A allow for impacts of floodwater inputs to be highlighted within the annual water budget. The isotopic mass balance model has revealed that groundwater and surface water inputs account for 60 %–71 % and 39 %–28 % of the total annual water inputs to lake A, respectively, which demonstrates an inherent dependence of the lake on groundwater. However, when considering the potential temporary subsurface storage of floodwater, the partitioning between groundwater and surface water inputs tends to equalize, and the lake A water budget is found to be more resilient to groundwater quantity and quality changes. Our findings suggest not only that floodwater fluxes to lake A have an impact on its dynamics during springtime but also significantly influence its long-term water balance and help to inform, understand, and predict future water quality variations. From a global perspective, this knowledge is useful for establishing regional-scale management strategies for maintaining water quality at flood-affected lakes, for predicting the response of artificial recharge systems in such settings, and for mitigating impacts due to land use and climate changes.

Evaluation of influent microbial immigration to activated sludge is affected by different-sized community segregation

Activated sludge (AS) microbial communities were analyzed for seasonal variation, a disturbance-recovery event, and separated small aggregates (SAG) to study the influent immigration effect using both neutral immigration model and mass-balance model with operational parameters. SAG differed with AS, and higher immigration impact on SAG was confirmed by both models. Adding the SAG community segregation in the latter model to evaluate the contribution of influent immigration to community disturbance-recovery showed increased impact of immigration.

Prominent role of sulfate reduction in robust sulfur retention in subtropical soil

Sulfur budgets in catchments indicated that about 80% of the deposited sulfur was retained in the subtropical soil, it alleviates the historical acidification caused by elevated deposition. The strong sulfur retention was attributed to the reversible sulfate adsorption in previous studies. Here we report that sulfate reduction is a prominent yet thus far overlooked mechanism for sulfur retention, based upon the comprehensive evidence of soil sulfur storage and multi-isotope within entire soil profile along a hydrological continuum in a typical subtropical catchment of China. Using a dual isotopic mass balance model, we determined that annual flux of reduction accounted for approximately 38% of sulfur retention, which was close to the proportion of reduced species in soil. Consequently, the release of sulfur legacy would be less serious with the decreasing sulfur deposition in China, compared to the projections only considering adsorption.