Mineral Mass Balance Research Articles

Mineral processing plant data reconciliation including mineral mass balance constraints

The operation of mineral processing units or plants is related to the mineral composition of the ore. However, unit performances are usually characterized in terms of metal content or recovery as this data is easier to be obtained rather than the mineral content. This paper presents a data reconciliation method that combines material balancing calculations and mineral stoichiometric information to estimate balanced mineral composition, chemical assays and flow rates in various streams of a mineral processing plant. The advantage of this method is evaluated by comparing the variance of the reconciled variables from this method to those obtained from usual data reconciliation methods. The estimated mineral composition leads to improved process performance evaluation.

A simple methodology for predicting the performances of hyaluronic acid purification by diafiltration

The performances of hyaluronic acid (HA) purification (yield, purity, permeate flow rate and productivity) in a semi-synthetic medium composed of salts, proteins/peptides by diafiltration through a 100kDa PES membrane were studied over 10 diavolumes (DV). The HA purity went from 3% to almost 100% with a yield in the retentate close to 100% at the end of the process. The permeate flow rate showed a peculiar trend due to the influence of charged microsolutes. DF mass balance applied to three groups of solutes (HA, peptides/proteins and charged microsolutes) allowed a good prediction of HA yield and purity in the course of DF. An equation of the permeate flux based on limit flux equation, correlations between mass transfer coefficient mineral concentration and mineral mass balance was proposed to predict the process productivity. Eventually, a methodology based on these equations was proposed to predict HA yield, purity and productivity. The methodology was validated with an actual Streptococcus zooepidemicus broth. Differences between calculations and experimental performances in term of yield, purity and productivity never exceeded 10%.

Free fatty acid and triacylglycerol forms of CLA isomers are not incorporated equally in the liver but do not lead to differences in bone density and biomarkers of bone metabolism

Few studies have compared differences between conjugated linoleic acid (CLA) in triacylglycerol (TG) and free fatty acid (FFA) form. This study assessed differences in liver incorporation, mineral mass balance, bone density, and biomarkers of bone metabolism between FFA and TG CLA diets. Rats (n=36) were fed a control (CTRL) or 1% CLA diet in FFA or TG form (1:1 mixture c9, t11: t10, c12). Liver content of c9, t11 CLA from FFA was greater than TG form and CTRL (FFA: 0.05±0.01 vs. TG: 0.02±0.01 vs. CTRL: 0.001±0.001% total fatty acids, P<0.0001). Liver t10, c12 CLA did not differ among groups (P=0.11). No diet differences among groups for growth, bone biomarkers or mass nor mineral balance were found. These findings suggest that c9, t11 CLA in FFA form is preferentially incorporated in the liver but fatty acid forms of CLA do not affect bone or mineral outcomes.

Experimental Measurements of Stress and Chemical Controls on the Evolution of Fracture Permeability

We explore how fracture permeability in confined tight carbonates evolves due to flow of reactive fluids. Core plugs of the Capitan Massive Limestone are saw-cut to form a smooth axial fracture that is subsequently roughened to control the fracture surface topography. Either distilled water or distilled water–ammonium chloride solutions are circulated through these plugs, where fracture roughness, inlet fluid pH, and confining stresses are controlled. Throughout the experiment we measure the fluid flow rate and chemical composition of the effluent fluid. Mass balance, conducted on the effluent fluid mass and on dissolved mineral components, independently constrains the mineral mass removal. We use an idealized lumped parameter model of asperity supported fractures undergoing simultaneous stress corrosion cracking-induced diffusion and free-face dissolution to infer theoretical rates of aperture loss or gain. This model incorporates the roles of confining stress, fracture contact area, and composition and reactivity of the permeating fluid while identifying zones of diffusion-dominated mass transfer within the fracture. These theoretical rates of aperture strain are compared to those inferred from the experimentally determined permeability evolution and permeating fluid mineral mass balance. By measuring in regimes of both increasing and decreasing permeability we quantitatively constrain the transition between fracture-gaping and fracture-closing modes of behavior. We parameterize this transition in permeability evolution by the ratio of mechanically to chemically controlled dissolved mass fluxes. The transition from regimes of closing to regimes of gaping occurs at unity ( $$\chi \approx 1$$ ) when stress and chemically driven mass fluxes are theoretically equal.

Spontaneous switching of permeability changes in a limestone fracture with net dissolution

Results are reported for water flow‐through experiments conducted on an artificial fracture in limestone at room temperature and under ambient confining stress of 3.5 MPa. Tests are concurrently monitored for mineral mass loss or gain and for changes in differential pressure between the inlet and outlet, throughout the 1500‐hour duration of the experiment. Periodic imaging by X‐ray computed tomography augments the fluid and mineral mass balance data and provides a third independent constraint on dissolution processes. The sample is sequentially circulated by water of two different compositions through the 1500‐hour duration of the experiment, the first 935 hours by sampled groundwater (pH ≈ 8), followed by 555 hours of distilled water (pH ≈ 6). Large changes in the differential pressure are recorded throughout the experiment, for the constant flow rate of 2 cm2/m; these are used as a proxy for recorded changes in fracture permeability, under invariant effective stress conditions. Mass of Ca and Mg were net‐removed throughout the experiment. During the initial circulation of groundwater, the differential pressure increased almost threefold and is interpreted as a net reduction in permeability as the contacting asperities across the fracture are removed and the fracture closes. With the circulation of distilled water, permeability initially reduced threefold and ultimately increased by 2 orders of magnitude as a “wormhole” developed in the sample. This spontaneous switch from net decrease in permeability to net increase occurred with no change in experimental conditions of flow rate or applied effective stress, and Ca was net dissolved throughout. This behavior is attributed to the evolving localization of mass removal, triggered as free‐face dissolution outcompetes stress‐mediated dissolution at the asperity contacts.

Spatial variations and controls of acid mine drainage generation

Spatial variations of historical and ongoing pyrite oxidation rates were quantified near the Nanisivik Mine on Baffin Island in northern Canada. The variations observed depend mainly on the degree of water saturation, pH and temporal trends in mineral reactivity. Maximum oxidation rates were observed in an untreated tailings spill, while minimum oxidation rates were noted for tailings deposited under water. Spatial trends in oxidation rates were in the order of three orders of magnitude. Spatial trends were only possible to quantify by a combination of closed chambers (well-drained conditions) and micro sensors (water-covered conditions). Oxygen uptake rates in tailings at various ages (up to 7 years) indicate a decrease by more than a factor of 3 over time. Total oxygen uptake over 7 years was calculated and found to be in a fair agreement with the overall pyrite depletion evaluated as high-resolution mineral mass balance (by quantitative powder X-ray diffraction).

Solute flux and mineral mass balance approaches to the quantification of plant effects on silicate weathering

The weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric CO 2 over geologic time, and vascular plants may have played an important role in this process. We have examined the role of plants in weathering in western Iceland by two methods: a solute flux approach and a mineral mass balance approach, using the chemistry of weathering products and of waters draining adjacent areas of basaltic rocks that are either barren (with a partial cover of mosses and lichens) or populated by trees. The study area was chosen to maximize vegetational differences and to minimize differences in microclimate, slope, and lithology, while avoiding hydrothermal waters and anthropogenic acid rain. Solute flux results, including data on cation uptake by growing trees, indicate that the rate of weathering release of Ca and Mg to streams is about 4 times higher in vegetated areas than in bare areas. Mineral mass balance results show that trees increase plagioclase weathering by a factor of 2 and pyroxene weathering by a factor of 10, possibly as a result of preferential weathering of pyroxene by the vegetation. Biomass-normalized weathering fluxes from the birch trees are greater than those from the conifers suggesting that angiosperms enhance weathering to a greater degree than gymnosperms. Results indicate a perpetual short-term sink for atmospheric C as tree-induced leakage of HCO (super -) 3 from the forest ecosystem to rivers and streams, in addition to the finite sink of C in forest biomass. The findings also suggest a major role for vascular plants, as they invaded upland portions of the continents between 410 and 360 my ago, in accelerating weathering and thereby lowering atmospheric CO 2 .