Multichannel reflectance spectral assaying of zinc and copper flotation slurries

This article extends the earlier work (Haavisto et al. 2008. Optical spectrum based measurement of flotation slurry contents. Int. J. Miner. Process. 88 (3–4), 80–88), where visible and near-infrared (VNIR) reflectance spectroscopy was used together with an X-ray fluorescence (XRF) analyzer to improve the assaying of zinc flotation concentrate. Especially the sampling interval of the assay could be drastically reduced by the presented approach. In this study, a multichannel VNIR spectrum analyzer is utilized to measure the spectrum of the seven most important slurry lines in copper and zinc flotation circuits. Recursive data-based modeling is applied to the VNIR spectrum data and XRF assays to calculate and adaptively maintain the calibration model. The accuracy of the VNIR assays is evaluated in all the lines, and the benefits of the obtained high frequency assays in detecting oscillations and sudden grade changes are demonstrated.     

Simultaneous optimization of the performance of flotation circuits and their simplification using the jumping gene adaptations of genetic algorithm-II: More complex problems

The binary-coded elitist non-dominated sorting genetic algorithm with the modified jumping gene operator (NSGA-II-mJG) is used to obtain global optimal solutions of flotation circuits. Several single-objective and multi-objective optimization problems are solved using the interconnecting cell linkage parameters (fraction flow rates) and the mean cell residence times as the decision variables. In the single-objective problem, the overall recovery of the concentrate stream is maximized for a desired grade of the concentrate. Two two-objective optimization problems are then solved. In one, the number of non-linking streams and the overall recovery of the concentrate are maximized simultaneously. This gives several simple circuits in a systematic manner with only marginally lower recoveries. In the other two-objective optimization problem, the overall recovery of the concentrate is maximized while the total cell volume is minimized. A three-objective problem (maximization of the overall recovery of the concentrate, maximization of the number of non-linking streams and minimization of the total cell volume) is then solved. All the problems constrain the grade of the product to lie at a fixed value. Finally, a complex and computationally intensive four-objective optimization problem is solved. The solution of several practical optimization problems in this study helps develop useful insights into the optimal solutions.     

Validation of a model for impact breakage incorporating particle size effect

Investigation of a breakage probability model published by Vogel and Peukert [Vogel, L. and Peukert, W., 2004. Determination of material properties relevant to grinding by practicable labscale milling tests. Int. J. Miner. Process., 74S, 329–338.] has led to a modification of their model to describe the degree of impact breakage, t₁₀. The modified model takes a form similar to the JKMRC prior art breakage model, but with particle size and breakage properties incorporated explicitly in the model.     

State of the art in the conceptual design of flotation circuits

The present study summarizes reports on optimal flotation circuits design over the period from 1989 to present. A review is made on the resolution characteristics of each study, leading to a classification of the approaches into four different groups, in which conclusions are based on either (A) mathematical solutions without binary variable, (B) mathematical solutions with binary variable, (C) heuristic solutions, or (D) genetic algorithms. These groups aim at a common scheme of resolution, varying in both flotation and milling models employed, characteristics of their superstructures, and functions which each study proposes to optimize, as well as the effects of the application of each strategy on the form of the solution of the circuit (selection of stages, selection of equipment, and dimensions of equipment).Within these either implicit or explicit multi-objective optimization problems there are challenges strongly related to the obtaining of better flotation and milling/classification models, as well as the treatment of uncertainty related to important parameters (kinetics, composition, external economic factors) and changes in previously established configurations using methods in which the designer's criteria influence the application of models and restrictions on the problem. Also, the incorporation of environmental issues needs more attention.     

Reply to ‘Comment on “The beginnings of hydrous mantle wedge melting” by Till et al.’ by Green, Rosenthal and Kovacs

The comment of Green et al. debates the interpretation of the temperature of the H₂O-saturated peridotite solidus and presence of silicate melt in the experiments of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) at <1,000?°C. The criticisms presented in their comment do not invalidate any of the most compelling observations of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) as discussed in the following response, including the changing minor element and Mg# composition of the solid phases with increasing temperature in our experiments with 14.5?wt% H₂O at 3.2?GPa, as well as the results of our chlorite peridotite melting experiments with 0.7?wt% H₂O. The point remains that Till et al. (Contrib Mineral Petrol 163:669–688, 2012) present data that call into question the H₂O-saturated peridotite solidus temperature preferred by Green (Tectonophysics 13(1–4):47–71, 1972; Earth Planet Sci Lett 19(1):37–53, 1973; Can Miner 14:255–268, 1976); Millhollen et al. (J Geol 82(5):575–587, 1974); Mengel and Green (Stability of amphibole and phlogopite in metasomatized peridotite under water-saturated and water-undersaturated conditions, Geological Society of Australia Special Publication, Blackwell, pp 571-581, 1989); Wallace and Green (Mineral Petrol 44:1–19, 1991) and Green et al. (Nature 467(7314):448–451, 2010).     

The settling of consecutive spheres in viscoplastic fluids

One of the factors contributing to the uncertainties involved in the estimation of particle settling velocity in viscoplastic fluids is the time-dependent effect where the viscous parameters of the fluid change as a particle flows through and shears the medium. These changes, particularly at low shear Reynolds numbers, are reflected in the settling velocity of a following sphere that is released some time after an initial one, with the following sphere having a significantly greater velocity. This study found that changes in both fall velocity and equivalent viscosity can be correlated satisfactorily by a power law equation to the dimensionless form of the time interval between releases, and the rheogram shape factor for the fluid. A collision of particles occurs in cases where the time interval between releases is small, after which the particles combine and travel at a terminal velocity. A new variable, β, which takes into account the different surficial stress of the combined spheres, was introduced to the correlation of Wilson et al. [Wilson, K.C., Horsley, R.R., Kealy, T., Reizes, J.A., Horsley, M.R., 2003. Direct prediction of fall velocities in non-Newtonian materials. Int. J. Miner. Process. 71, 17–30] β was found to depend on the rheogram shape factor for the fluid and the shear Reynolds number for the particle. The validity of this approach was supported by experimental data.     

Small-scale spatial variation of the stress field in the back-arc Aegean area: Results from the seismotectonic study of the broader area of Mygdonia basin (N. Greece)

In the present work a detailed seismotectonic study of the broader area of the Mygdonia basin (N. Greece) is performed. Digital data for earthquakes which occurred in the broader Mygdonia basin and were recorded by the permanent telemetric network of the Geophysical Laboratory of the Aristotle University of Thessaloniki during the period 1989–1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information. Fault plane solutions for the 3 main shocks of Volvi (23/05/78, M_W = 5.8 and 20/06/78, M_W = 6.5) and Arnaia (04/05/95, M_W = 5.8) events and the 1978 aftershock sequence were additionally used. Moreover, data from two local networks established in the Mygdonia basin were also incorporated in the final dataset.Determination of the stress field was realized by the use of the method of Gephart and Forsyth [Gephart, J.W., Forsyth, D.W., 1984. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence: Jour. Geophys. Res., v.89, no. B11, p. 9305–9320] for the stress tensor inversion and the results were compared with independent estimates based on the calculation of the average moment tensor [Papazachos, C.B.,Kiratzi, A.A., 1992. A formulation for reliable estimation of active crustal deformation and its application to central Greece. Geophys. J. Int. 111, 424–432]. The obtained stress results show a relatively good agreement between the two approaches, with differences in the azimuth of the dominant extension axis of the order of 10°. Furthermore, comparison with independent information for the mean stress axes provided by the study of kinematics on neotectonic faults [Mountrakis, D., Kilias, A., Tranos, M., Thomaidou, E., Papazachos, C., Karakaisis, G., Scordilis, E., Chatzidimitriou, P., Papadimitriou, E., Vargemezis, G., Aidona, E., Karagianni, E., Vamvakaris, D. Skarlatoudis, A. 2003. Determination of the settings and the seismotectonic behavior of the main seismic-active faults of Northern Greece area using neotectonic and seismological data. Earthquake Planning and Protection Organisation (OASP) (in Greek)] shows a similar agreement with typical misfit of the order 10°. The stress inversion method was modified in order to select one or both nodal planes of the focal mechanism which corresponds to the “true” fault plane of the occurred earthquakes and was able to select a single fault plane in the majority of examined cases. Using this approach, the obtained fault plane rose diagrams are in agreement with results from various neotectonic studies. Moreover, several secondary active fault branches were identified, which are still not clearly observed in the field.     

A new approximation for pore pressure accumulation in marine sediment due to water waves

The residual mechanism of wave‐induced pore water pressure accumulation in marine sediments is re‐examined. An analytical approximation is derived using a linear relation for pore pressure generation in cyclic loading, and mistakes in previous solutions (Int. J. Numer. Anal. Methods Geomech. 2001; 25 :885–907; J. Offshore Mech. Arctic Eng. (ASME) 1989; 111 (1):1–11) are corrected. A numerical scheme is then employed to solve the case with a non‐linear relation for pore pressure generation. Both analytical and numerical solutions are verified with experimental data (Laboratory and field investigation of wave– sediment interaction. Joseph H. Defrees Hydraulics Laboratory, School of Civil and Environmental Engineering, Cornell University, Ithaca, NY, 1983), and provide a better prediction of pore pressure accumulation than the previous solution (J. Offshore Mech. Arctic Eng. (ASME) 1989; 111 (1):1–11). The parametric study concludes that the pore pressure accumulation and use of full non‐linear relation of pore pressure become more important under the following conditions: (1) large wave amplitude, (2) longer wave period, (3) shallow water, (4) shallow soil and (5) softer soils with a low consolidation coefficient. Copyright © 2006 John Wiley & Sons, Ltd.     

Under stress permeability determination of the Meuse/Haute-Marne mudstone

In the underground waste isolation projects such as the ANDRA'one in the site of Bure, the transport properties of the surrounding rock mass is of fundamental importance. To measure very low permeability, we use the modified version of the pulse test proposed by Hsieh et al. [Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245-252] which enables the intrinsic permeability, k, and the specific storage coefficient, S_s, of rocks such as mudstone to be characterized. In this paper, the special effort performed on the laboratory apparatus design, to ensure a good sensitivity of the rock response with respect to both parameters, k and S_s, is presented. In addition, two parameters identification procedures are proposed: the graphical method given by Hsieh et al. [Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245-252] and a parameter identification based on the solution of an inverse problem. The efficiency of the apparatus design and the parameters identification procedures is then demonstrated though some pulse tests performed on the Meuse/Haute-Marne mudstone.     

A MILP model for design of flotation circuits with bank/column and regrind/no regrind selection

A method for the design of flotation circuits is presented. The design problem is represented by several superstructures. The first superstructure represents separation tasks (STS), which include: feed processing superstructure (FPS), concentrate processing superstructure (CPS), and tail processing superstructure (TPS). The FPS commonly uses a single stage, i.e., rougher. The CPS represents the circuit needed to carry out the cleaner task, and the TPS represents the circuit needed to carry out the scavenger task. These superstructures are flow networks between several separation stages. In each separation stage two kinds of cells are allowed, bank and column. In several streams in the CPS and TPS, the incorporation of regrind mills is also included.     

The geotherm of the lithosphere beneath Qilin, SE China: a re-appraisal and implications for P–T estimation of Fe-rich pyroxenites

The Qilin geotherm established by Xu et al. [Xu, X.S., O'Reilly, S.Y., Zhou, X.M. and Griffin, W.L., 1996. A xenolith-derived geotherm and the crust-mantle boundary at Qilin, southeastern China. Lithos, 38: 41–62.] using the Ellis and Green [Ellis D.J. and Green D.H., 1979. An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria. Contrib. Mineral. Petrol., 71: 13–22]/Wood [Wood B.J., 1974. Solubility of alumina in orthopyroxene coexisting with garnet. Contrib. Mineral. Petrol. 46: 1-15] combination is in need of revision on the basis of re-evaluation of geothermobarometers, comparison of calculated pressures and temperatures with experimentally determined phase relationships and geological/geophysical data. The invalid assumption that all iron is present as Fe²⁺ in minerals, and the thermal destruction of equilibrium Fe–Mg exchange between clinopyroxene and garnet that may have resulted from heating of the Qilin xenoliths by the host magma resulted in unrealistically high temperatures estimated by the Ellis and Green's thermometer. An important implication arising from this study is that care must be taken when applying thermobarometers to Fe-rich pyroxenites for the purpose of geotherm construction and a comprehensive analysis is often required.     

Surface chemical mechanisms of inadvertent recovery of chromite in UG2 ore flotation: Residual layer identification using statistical ToF-SIMS analysis

In the UG2 ore (Bushveld Complex, South Africa) flotation, normally more than 3% of the gangue minerals, principally chromite with talc and pyroxene, report to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Previous studies have identified residual talc-like layers on orthopyroxene surfaces in Merensky ore flotation contributing to inadvertent flotation of relatively large particles (20–150 µm) of this mineral. Chromite (75–150 µm) from flotation of UG2 ore has been similarly examined. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu, Pb, Ni and collector (IBX and DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. The flotation rate of coarse chromite correlates with the exposures of magnesium and silicon in patches on the chromite surface; higher exposures give earlier flotation. Conversely, there is a negative correlation with signals corresponding to the chromite surface, i.e. Cr, Fe, Al. Flotation of chromite without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, similar to those found on orthopyroxene surfaces, probably from partial alteration, explain this flotation mechanism.     

云南大屯锡粗精矿工艺矿物学研究

以云南大屯选矿厂锡粗精矿为研究对象,采用化学分析、X射线衍射分析及光学显微镜分析等手段对该粗精矿的化学组成、矿物组成、矿物嵌布粒度特征等进行了详细的研究。结果表明,锡粗精矿中有价元素锡的品位为13.80%,锡矿物主要以锡石形式产出。锡粗精矿中TFe含量为30.78%,主要以褐铁矿、磁黄铁矿的形式存在,磁黄铁矿是导致粗精矿含硫高的主要原因。锡粗精矿中主要的脉石矿物有白云石、透闪石、电气石、石英、白云母、萤石等,且脉石矿物与锡石均有不同程度的毗邻连生、包裹共生关系。本次工艺矿物学研究认为,大屯选矿厂锡粗精矿宜采用浮选预先脱硫,除去其中的硫化物,再对浮选尾矿采用重选工艺提高锡品位和回收率。该研究结果可以为大屯选矿厂工艺流程改造和合理开发利用锡资源提供科学依据。     

Reply to comments on “Explicit versus implicit front advancing schemes for the simulation of hydraulic fracture growth” (Int. J. Numer. Anal. Methods Geomech., 2019, 43 (6), 1300–1315)” by Prof. Linkov

We reply to Prof. Linkov comments on our article entitled “Explicit versus implicit front advancing schemes for the simulation of hydraulic fracture growth” (Int. J. Numer. Anal. Methods Geomech., 2019, 43 (6), 1300–1315). We present additional results indicating that both the implicit and explicit front advancement schemes are robust even in the case of a large stress contrast.     

An empirical method for the determination of single ion hydrogen isotope salt effects in aqueous electrolyte solutions

An empirical method is presented that allows the determination of the individual contributions of anions and cations to the effect of dissolved salts on hydrogen isotope fractionation in aqueous systems (isotope salt effect). The method is solely based on experimental data and does not involve the choice of arbitrary reference values or theoretical assumptions. Plotting experimental liquid–vapor D/H fractionation factors for aqueous solutions of sodium salts vs. O–D stretching frequencies of water molecules in the hydration shells of the anions shows an excellent linear correlation. The distance between this line and the pure water liquid–vapor fractionation data point in the same plot gives the cation contribution to the isotope salt effects. The anion contribution can then simply be derived as the difference between the total salt effect and the cation salt effect. The validity of the concept is demonstrated using precise literature data for the O–D stretching frequencies in the hydration shells of individual ions at 20°C [Bergström, P.A., 1991. Single ion hydration properties in aqueous solution: a quantitative infrared spectroscopic study. PhD Thesis. Uppsala University] and for the liquid–vapor hydrogen isotope fractionation between aqueous solutions and water vapor at the same temperature [Stewart, M.K., Friedman, I., 1975. Deuterium fractionation between aqueous salt solutions and water vapor. Journal of Geophysical Research 80, 3812–3818]. Within the limits of experimental uncertainties, the data set shows internal consistency. Cation salt effects, 1000 ln Γ at 20°C, are (in per mil per mole per liter, using the convention of Horita et al. [Horita, J., Cole, D.R., Wesolowski, D.J., 1993a. The activity–composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: II. Vapor–liquid water equilibration of mixed salt solutions from 50–100°C. Geochimica et Cosmochimica Acta 57, 4703–4711]): Na⁺+0.7; K⁺+0.7; Mg²⁺+6.5; Ca²⁺+1.8; Al³⁺+12. The salt effect of H⁺ cannot be determined unequivocally. The combined effect of the fractionation of H⁺ itself plus its salt effect is +4.9. Anion effects are +1.4 for Cl⁻, +2.7 for Br⁻, +3.5 for I⁻ and −1.4 for SO₄²⁻. Further single anion salt effects are being predicted as −1.8 for F⁻, +4.9 for NO₃⁻, +6.9 for ClO₄⁻ and +5.4 for the triflate ion (CF₃SO₃⁻).     

Proposed upgrading techniques for East Sibaiya phosphorites,Aswan area,southern Egypt

The Late Cretaceous (Campanian-Maastrichian), low-grade phosphorite sequence of East Sibaiya, Aswan area, which is known as the Duwi (phosphate) or Sibaiya Formation, is usually intercalated with marl, oyster limestone, and chert beds. These strata, which crop out in a generally east–west trending belt spanning the middle latitudes of Egypt, are phosphorite-rich sediments and of great economic importance. Representative samples were collected from the investigated area at several localities (e.g., Umm Tundubah-2 and Wadi El-Batur) and 200 kg of phosphate rocks was used for upgrading processes of low-grade phosphorites of the East Sibaiya area. The upgrading processes included two techniques: the first technique (gravity separation) comprises crushing, sieving, gravity separation by a shaking table, and magnetic separation. This technique raised the P₂O₅ in the head sample from 24.73 to 31.91% as a phosphate concentrate. The second technique (flotation technique) depends on certain flotation parameters such as pH, grain size, and phosphate collector dose (i.e., oleic acid). The flotation technique increased the P₂O₅% from 24.73 to 31.16% as a final product of the phosphate concentrate. These data were confirmed by X-ray fluorescence analyses of major elements.     

ToF-SIMS-derived hydrophobicity in DTP flotation of chalcopyrite: Contact angle distributions in flotation streams

Particle hydrophobicity has been derived from Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements and its impact on the flotation behaviour of chalcopyrite investigated. Batch flotation tests were performed using a dithiophosphate-type of collector in different concentrations. Three flotation regimes were studied using particle size ranges of 20–38 μm, 75–105 μm and 150–210 μm. The individual particle contact angle, and hence, the distribution of contact angles of chalcopyrite within feed, concentrate and tail flotation samples has been determined using ToF-SIMS secondary ions. The effects of particle size and hydrophobicity on the flotation behaviour have been investigated using this new approach. The hydrodynamic effects of the particle size were highlighted by the different distributions of contact angles obtained for each concentrate size fraction, with fine and coarse sizes requiring higher average contact angles to float. This effect was overtaken by hydrophobicity when a high collector concentration was used. The broad distribution of contact angles observed in all samples, i.e. heterogeneity in hydrophobicity, has significant consequences for interpreting flotation behaviour. The methodology of analysis conducted in this study was applied to real ore and can be used as a quantitative, diagnostic tool for examining surface chemical factors affecting hydrophobicity. This new technique has promise and may advance the understanding of mechanisms, which may lead to better control strategies for improving flotation performance. Furthermore, any mineral–collector system can be targeted, provided appropriate calibration is performed.     

Potential use of model predictive control for optimizing the column flotation process

A constrained model predictive control (MPC) strategy is proposed to deal with the problem of optimizing flotation column operation using secondary variables. Froth depth, collection zone gas hold-up and bias rate are selected as secondary variables to be controlled whereas tailing, wash-water and gas flow rate are used as manipulated variables. The control problem was formulated in order to minimize the tracking error of the gas hold-up and bias rate by maintaining gas flow rate, wash-water flow rate and bias rate within their operational limits. In particular, a strategy was conceived to optimize the column flotation process based on establishing an unreachable high set point for the gas hold-up (which is equivalent to maximizing the bubble surface area available for particle collection at a given flotation reagent dosage and thus recovery), while simultaneously satisfying operational constraints (such as ensuring a positive bias rate to prevent gangue entrainment and therefore concentrate grade deterioration). Several other operational constraints on wash-water, gas rate, gas hold-up and bias rate were considered, their use being justified from a processing point of view. Since this study deals with the hydrodynamic characteristics of flotation columns, a pilot flotation column working with a two-phase system is sufficient to demonstrate the advantages of using predictive control for this process optimization.     

Renaissance of the astronomical theory of climatic change

Book reviewed in this article:
Berger, A., Imbrie, J., Hays, J., Kukla, G. and Saltzman, B. (eds.) 1984: Milankovitch and Climate. Understanding the Response to Astronomical Forcing .     

A compartment model for the mass transfer inside a conventional flotation cell

A model is developed by taking into account the simultaneous mechanisms of true flotation and entrainment in a conventional flotation cell. The total volume of the cell is divided into three compartments: pulp collection zone, pulp quiescent zone and froth region, with the mechanisms being modeled as occurring at the same time but originating at different places: true flotation from the collection zone and entrainment from the quiescent one. A particle is referred to as suspended in water or attached to an air bubble, depending upon its original state before crossing the pulp–froth interface (whether or not it remains in that state all the way to the concentrate launder). The model is obtained by solving a set of equations describing the mass conservation of solids and water between adjacent compartments. The principal mass transfer factors are identified as: the flotation rate constant, the mean residence time in the collection zone, the froth recovery of attached particles, the degree of entrainment through the froth and the water recovery from the feed to the concentrate. The development presented here allows the intricate nature of the mass transfer in a flotation cell to be reduced to one single equation, overcoming the need of numerical methods for simulation purposes. Moreover, it is shown that reliable prediction of grade and recovery can be obtained without detailed information on the pulp hydrodynamics or on any froth sub-process either than drainage, bubble bursting and bubble coalescence.