Precipitation Of Goethite Research Articles

Speciation Controls the Kinetics of Iron Hydroxide Precipitation and Transformation at Alkaline pH.

The formation of energetically favorable and metastable mineral phases within the Fe-H2O system controls the long-term mobility of iron complexes in natural aquifers and other environmentally and industrially relevant systems. The fundamental mechanism controlling the formation of these phases has remained enigmatic. We develop a general partial equilibrium model, leveraging recent synchrotron-based data on the time evolution of solid Fe(III) hydroxides along with aqueous complexes. We combine thermodynamic considerations and particle-morphology-dependent kinetic rate equations under full consideration of the aqueous phase in disequilibrium with one or more of the forming minerals. The new model predicts the rate of amorphous 2-line ferrihydrite precipitation, dissolution, and overall transformation to crystalline goethite. It is found that the precipitation of goethite (i) occurs from solution and (ii) is limited by the comparatively slow dissolution of the first forming amorphous phase 2-line ferrihydrite. A generalized transformation mechanism further illustrates that differences in the kinetics of Fe(III) precipitation are controlled by the coordination environment of the predominant Fe(III) hydrolysis product. The framework allows modeling of other iron(bearing) phases across a broad range of aqueous phase compositions.

Thermodynamics of the α-FeOOH (goethite)-ScOOH solid solution

Scandium (Sc) is a rare element that finds uses in modern technologies. Thermodynamic properties of Sc phases could help in the development of innovative technologies to extract Sc from mining waste. In this work, we investigated the FeOOH–ScOOH solid solution with the goethite structure. The end members and five intermediate compositions were synthesized and characterized. The lattice parameters show that the solid solution is non-ideal, with complex behavior induced by the Fe–Sc substitution. The excess unit-cell volume deviates negatively for the Sc-rich region, and positively for the Fe-rich region from the ideal behavior (Vegard’s law). Enthalpies of dissolution were determined by acid-solution calorimetry in 5 mol·dm-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot \\hbox {dm}^{-3}$$\\end{document} HCl at T = 343.15 K. Enthalpies of mixing (ΔmixH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _{mix}H$$\\end{document}), calculated from the experimental data, are small and positive. The available data allow for fitting the data as ΔmixH=Wx(1-x)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _{mix}H = W x (1-x)$$\\end{document}, with the mixing parameter W=15.2±\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W = 15.2\\pm$$\\end{document}1.0 kJ·mol-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot \\hbox {mol}^{-1}$$\\end{document}. Using ΔfGo\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _fG^o$$\\end{document} of ScOOH from earlier literature, we calculated a Lippmann diagram that shows that Sc should strongly partition into the aqueous phase upon goethite precipitation. The field observations from lateritic profiles show that Sc is primarily harbored by goethite via adsorption. It seems that under weathering conditions, thermodynamically driven partitioning of Sc3+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Sc}^{3+}$$\\end{document} into the aqueous phases and its subsequent adsorption onto goethite surfaces controls the mobility of Sc in the weathering profiles.

Hydrogeochemical analysis of processes affecting HCH removal using ZVI-based treatment technology

In the 1960s, ca. 3000–5000 tons of HCH residue were disposed of in an overburden dump at the Hájek kaolin/uranium mine site (Czech Republic). The dump leachate, which has a 136 μg/l average total content of hexachlorocyclohexane (HCH) isomers, discharges into a local creek and contaminates the ecosystem. A full-scale prototype for the treatment of dump leachate comprised three sequential stages: 1) permeable reactive modules filled with macro-zerovalent iron (mZVI), 2) a biosorption module and 3) an aerobic wetland module. After commissioning, HCH removal efficiency reached 95%, but decreased to 70% over the following 230 days, primarily due to the efficiency of the mZVI modules dropping from 76% to 39%. Hydrogeochemical analysis and geochemical modelling revealed that the reduction in efficiency was mainly caused by passivation of mZVI surfaces and clogging of mZVI pore spaces through precipitation of goethite, calcite and rhodochrosite, or siderite and magnetite instead of goethite where boundary conditions for O2 differed. XRD analysis of the solid phase from the mZVI modules confirmed the geochemical modelling results. The major part of the precipitated products (46–66 wt%) comprised a ferric hydroxide amorphous phase, especially in the initial mZVI module inlet, with goethite the second most abundant precipitate (10–40 wt%). Siderite and calcite also mainly precipitated in the initial module inlet. In conclusion, mZVI appears to be a suitable reductant for HCH; however, the longevity of the ZVI-based treatment system was negatively affected by precipitates in the presence of high concentrations of iron, manganese and carbonate species.

Reactive transport modeling of the Aquifer Thermal Energy Storage (ATES) system at Stockton University, New Jersey during seasonal operations

Hydrogeochemical processes associated with Aquifer Thermal Energy Storage (ATES) operations can often impact the system performance owing to mineral precipitation either at the wellbore or in the aquifer owing to changes in temperature and fluid disequilibria. Although failure of ATES systems due to mineral precipitation ("fouling") is common, predictive reactive-transport models have rarely been applied to plan their design and operation. The objective of this study is to develop a reactive-transport model by coupling thermal, hydrological, and chemical (THC) processes to evaluate effects of introduced atmospheric oxygen on water chemistry, mineral precipitation/dissolution, porosity, and permeability changes associated with an ATES system at Stockton University (New Jersey, USA). The THC model builds on a Thermal-Hydrological-Mechanical (THM) model of the site (Smith et al., 2021) that evaluated system failure owing to possible fracturing in the caprock or around the wellbore. The causes of the system failure are not known – potential causes include hydraulic fracturing owing to elevated pump pressures that took place, a flow pathway created by one of the boreholes, or a pre-existing natural hydrologic connection between the upper unconfined aquifer and the ATES aquifer, any of which could have led to oxygenated water entering the reservoir and causing the observed Fe-oxide fouling on well screens. The THC model is used to evaluate some of the hypotheses and observations regarding system failure owing to geochemical processes.The reactive-transport code TOUGHREACT V4 (Sonnenthal et al., 2021) was used to model the THC processes during seasonal heating and cooling operations at the Stockton ATES site over 6 years of operation. In the THC simulations, the primary effects on geochemistry were observed when the injection water is saturated with atmospheric oxygen. Simulations show greater precipitation of goethite near the cold wells as compared to the warm wells. Although volume fractions of Fe-hydroxides were relatively small, the model was aimed at processes in the aquifer at the scale of meters and larger rather than at the scale of mm or cm (i.e., a well screen). Kaolinite is the dominant precipitating phase, also around the cold wells. Illite dissolves near the cold wells and precipitates near the warm wells. There is a net decrease in the porosity near the cold wells and increase near the warm wells, although a slight amount of thermal contraction near the cold wells and expansion near the warm wells is responsible for a significant proportion of the porosity change. Owing to the coarse discretization of the numerical grid near the wells (compared to the screen thickness) the magnitude of permeability changes at the wellbore are likely underestimated. The reactive transport model in this study can be used for characterization of aquifers, optimizing the operational parameters (temperature, pressure, pH etc.), and planning of mitigation strategies for ATES systems.

Relationships between morphological facies and the evolutionary processes of petroplinthites in the Southern Espinhaço Range (SE-Brazil)

Morphological facies of petroplinthites describe how soil components such as the soil matrix, nodules, pores, and coatings relate to each other in space. French scientists have extensively used such descriptions to interpret evolutionary processes and stages of petroplinthites (laterites, ferruginous duricrusts, ironstones) in Central and Western Africa. However, there has been little progress using the interpretation of petroplinthite facies in other parts of the world. This study explores the protocol in Brazilian petroplinthites with the aim of defining processes and identifying evolutionary stages based on analysis of the morphological differences in the petroplinthites from a pedogenetic perspective. The studies were concentrated in the Southern Espinhaço Range, southeast Brazil, and covered Petric or Pisoplinthic Plinthosol (Petroferric Oxisols) profiles with a wide morphological variety of petroplinthites. Based on a literature review, the aim was to standardize concepts and define the different morphological facies, before applying them to the petroplinthites of the study area. Geochemical and mineralogical analyses were added to the description of the facies to interpret the main pedogenetic processes and evolutionary sequences among the profiles. As such, macro and micro morphological descriptions were carried out in association with geochemical maps using SEM-EDS, and specific mineralogical characterization was performed using an electronic microprobe to characterize the main morphological facies. XRD, XRF, and magnetic susceptibility analyses were used to interpret the main formation, transformation, and degradation processes of the petroplinthites. The integration of these analyses enabled the association of the morphological facies with the petroplinthite evolutionary processes. Thus, while lamellar facies are shown to be directly associated with saprolitization processes, nodular and massive facies generally represent intense lateritization. Protopisolithic facies are commonly associated with transformation processes, with goethite precipitation and re-cementation of the matrix, while pisolithic facies are formed through degradation processes with intense mineral dissolution. Recovering the protocol for associating macro and micro morphological facies with geochemistry and mineralogy enabled improved interpretation of the genesis of petroplinthites, with clearer and more objective identification of the evolutionary stages, as well as their relationship with the landscape and the hydrological systems and environmental conditions.

Separation of Iron from ZnSO4 solution by oxygen pressure-enhanced hydrothermal precipitation

ABSTRACT This study presented a method for removing iron (Fe) from zinc (Zn) sulfate solution utilising an oxygen (O2) pressure-enhanced goethite process. The study investigated the effects of O2 pressure, reaction temperature (T), pH value, and reaction time (t) on the Fe removal process. The results indicated that the oxidation rate increased with increasing T and O2 pressure. The goethite obtained at an O2 partial pressure of 0.2 MPa exhibited higher Fe content and a distinct acicular morphology, containing 55.7% Fe, 5.4% Zn, and 1.9% Sulphur (S). The increase in temperature from 90°C to 110°C accelerated the Fe hydrothermal precipitation, enhancing the Fe content in the goethite from 55.7% to 57.1%. The goethite products with 56.4% Fe content exhibited 95.0% crystallinity at a pH of 3.2, with a tendency for particle aggregation at lower crystallinity levels. The goethite precipitation occurred within the pH range of 2.2−3.5. Furthermore, as the reaction time increased, the hydrothermal precipitation particles increased in size and exhibited higher Fe content. The proposed method modified the O2 mass transfer process, increasing its solubility to enhance the Fe2+ oxidation rate, facilitating the controlled acicular α-FeOOH production with excellent crystallization performance.

Application of inverse modelling for prediction of the surface water chemistry of the ekulu river in enugu, southeastern nigeria

Surface water chemistry evolution of Ekulu River was conducted by inverse geochemical modelling using the PHREEQC computer program. In this study, samples were collected from the Ekulu river at 100m intervals, and were taken to the laboratory for major anions and cations, heavy metal and bacterial content analyses. Inverse geochemical modelling results reveal that the river evolved as a result of dissolution of siderite, quartz, gypsum, galena, sphalerite, pyrolusite and precipitation of goethite and pyrite. The Piper diagram indicates Calcium-Chloride water type, with high Ca2+ + Mg+ and Cl- + SO42 contents, which is typical of water originated from gypsum dissolution and mine drainage. The results of the analyses show that the water cannot be recommended for drinking because the E. coli and coliform contents are higher than the permissible limits. The water chemistry of Ekulu river is as a result of secondary minerals dissolution and mine drainage from Onyeama coal mine whereas the microbial content resulted from pollution from recent faeces.
 

Iron Removal as Goethite from Synthetic Laterite Leach Solutions.

The aim of this study was to precipitate goethite from high-iron(II)-bearing atmospheric and heap leach solutions of lateritic nickel ore generated either by reductive leaching of the ore or by reducing Fe(III) of the leach solution to Fe(II) using a suitable reducing agent and to understand the Ni and Co losses during the iron precipitation. Removal of Fe was carried out using an oxidative hydrolysis technique targeting goethite precipitation from a synthetic laterite leach solution containing Fe as ferrous (Fe(II)), Al, Mg, Ni, Co, Cr, Mn, Cu, and Zn using limestone as the neutralizing agent and air as an oxidant. The behavior of goethite precipitation and the losses of Ni and Co were examined under various conditions of pH, temperature, and Fe concentration. The precipitation of Fe increased with increasing pH, temperature, and feed Fe(II) concentration. Precipitation at pH ∼4.0-4.1 (measured at ambient temperature) and 90 °C resulted in ∼96-97% Fe removal from a feed solution containing more than 50 g/L Fe(II), giving ∼1 g/L Fe in the final liquor. Goethite formation was confirmed as a result of the Fe precipitation, and it appeared to take place via ferrihydrite/schwertmannite intermediate phases. The crystallinity of the goethite increased with time, temperature, and feed Fe(II) concentration. The goethite precipitate was found to be associated with an alunite phase. Losses of Ni and Co during Fe precipitation increased with pH, temperature, and feed Fe(II) concentration. The losses were significant above pH 4 and found to be ∼7-22% Ni and 4-19% Co in the pH range 4.1-5. The test results indicate that efficient Fe removal via goethite precipitation can be achieved from reduced atmospheric and heap leach solutions of laterite ore; however, careful pH control is required to minimize the loss of Ni and Co during this precipitation.

Origin of ooids, peloids and micro-oncoids of marine ironstone deposits in Western Siberia (Russia)

This study investigates the authigenically formed Late Cretaceous and Paleogene marine ironstones in Western Siberia (Russia) based on petrographic and spectroscopic investigations. In the Upper Cretaceous Kuznetsovo, Ipatovo, Slavgorod, Gan'kino and Paleogene Lyulinvor Formations of the West Siberian ironstone basin, there are three main ore horizons, known as the Narym, Kolpashevo, Bakchar layers. The marine succession predominantly comprises ooidal or peloidal ironstones, glauconitolites, glauconitic rocks, sandstones, siltstones, claystones and gritstones. The ooidal ironstone exhibits predominantly abiogenic precipitates with subordinate microbial signatures, including micro-oncoids, relicts of lipids, carbohydrates and microfilaments. Iron-rich ooids, peloids and micro-oncoids formed primarily by adsorption of iron and occasionally by microbial iron-oxidising and sulphate-reduction actions. The abiogenic formation of ooid and peloid depends on physico-chemical conditions of environment during ion adsorption. While berthierine-goethite in ooid cortex formed in an oxic or dysoxic environment, siderite laminae therein represent an anoxic condition. Microbial mediation influenced the precipitation of berthierine and goethite, pyrite, siderite, greigite, pyrrhotite, wurtzite, barite, As-Ni-Co-Fe sulphide, and probably monazite. Siderite, pyrite, and to a lesser extent greigite and pyrrhotite formed exclusively within organic remains. Goethite with a high content of phosphate within micro-oncoids probably formed with the mediation of microbial activities. Bacterial microfilaments and Raman peaks of lipids and carbohydrates strongly support a bacterial origin of micro-oncoids. Abundant intraclasts at the base of the Ipatovo Formation that marks the Coniacian-Santonian boundary, and those within the Lyulinvor Formation that marks the Palaeocene-Eocene boundary, correspond to active tectonics, which provided an enhanced supply of metal-rich nutrients. Distribution of trace elements in the main iron-rich minerals supports a hydrothermal source of iron and other metals for iron-rich ooids and peloids in Western Siberia. The study of the Meso-Cenozoic marine ironstones provides insights into the biotic or abiotic processes involved in case of Precambrian banded iron formations (BIFs).

Insight into the magnetic properties of Pb-dopped iron oxide nanoparticles during Fe(III) bio-reduction by Shewanella oneidensis MR-1

Anthropogenic activities have led to a significant accumulation of Pb in the environment, posing a threat to ecosystems. Iron oxides that display magnetic properties are ubiquitous in the environment and Pb partitioning onto these minerals is considered one of the most critical geochemical processes controlling its environmental fate. In anoxic environments, iron oxides undergo redox cycling due to biotic and abiotic routes, resulting in their transformation/dissolution and evolution of their magnetic characteristics. However, there is still a lack of knowledge on the impact of Pb on the dynamic of iron oxides bioreduction. Furthermore, there is little information available regarding the nature of biogenic minerals and their magnetic signatures.Here we incubated Pb-bearing ferrihydrites (Fh_Pb) with various Pb/(Fe + Pb) molar ratios (i.e., 0, 2 and 5%) with the iron-reducing bacterium Shewanella oneidensis MR-1, for 21 days.XRD analyses of the initial Fh_Pb displayed characteristic features of Fh and a decrease of magnetization in the presence of Pb. During the bio-reduction process, Pb doping led to a drop in the rate and extent of reduction. At the end of the incubation period, the analysis of the aqueous solutions revealed a minor proportion of Pb in solution, indicating that a significant proportion of the Pb is sorbed onto the biogenic minerals. Magnetite (95%) and siderite (5%) formed during the bioreduction of Fh, while magnetite (~80%) and goethite (~20%) precipitated in the presence of Pb as revealed by transmission Mössbauer spectroscopy. Furthermore, the size of the magnetite particles decreased from about 11 nm in absence of Pb to 6 nm with 2% of Pb-bearing, while 5% of Pb led to particles too small to be quantified with our TEM measurements. The combined effect of the decrease in particle size of magnetite, substitution of Pb and the precipitation of goethite in the Pb-dopped assay led to a significant decrease of magnetization at room temperature. Overall, this study highlights the effect of Pb on iron oxides bio-reduction and transformation processes and the sensitivity of magnetism to serve as a monitoring method.

Cenozoic weathering of fluvial terraces and emergence of biogeographic boundaries in Central Amazonia

The study of paleofluvial dynamics is crucial to understand the role of rivers as biogeographic boundaries in Amazonia during the Cenozoic. In central Amazonia, Mesozoic and Cenozoic fluvial deposits - Alter do Chão, Iranduba and Novo Remanso Formations - host supergene iron oxides and record changes in the distribution of flooded and non-flooded (upland) environments. Geochronological data on these deposits are still scarce to constrain past landscape changes. Therefore, in this study we investigate iron oxides precipitated within weathering profiles developed on ancient fluvial terraces to access the interplay between flooded and non-flooded environments in central Amazonia. We aimed to trace the history of abandonment of alluvial plains and the subsequent weathering of lowland sediment deposits during the Cenozoic. We identified at least two main periods of iron oxide precipitation: (1) one starting before ~42 Ma and ending at ~18 Ma; and (2) a well-defined humid and weathering prone phase between ~8 and 1 Ma. Dominant goethite precipitation marks a major climatic shift towards more humid conditions from ~3 Ma. The increase in water discharge of the Negro and Solimões rivers possibly promoted fluvial incision and conversion of floodplains into long-lasting upland terrains as indicated by the development of lateritic weathering profiles. This major phase of upland expansion corroborates upland birds phylogenetic data, which indicate the emergence of a major biogeographic barrier in central Amazonia during late Pliocene/Pleistocene. • Refining the age of the fluvial sedimentary units in central Amazonia • Multiple Cenozoic discrete weathering phases in central Amazonia • Linking weathering phases with fluvial landscape changes • Constraining the emergence of a major biogeographic boundary

The significance of outcrop analog data for reservoir quality assessment: A comparative case study of Lower Triassic Buntsandstein sandstones in the Upper Rhine Graben

Subsurface reservoir quality assessments are among the most important workflows in reservoir geology. The application has been standard practice in the hydrocarbon industry and is also adopted for geothermal reservoir systems hosted in clastic rocks. With the emergence of fluid mining for metals, such as lithium for the energy transition, yet another field may adopt the standard practice. However, as drill cores and hard geological data from the subsurface are expensive commodities they may be substituted by outcrop analog studies to fill in data gaps in the understanding of the deep subsurface. However, reservoir quality controls, such as pore-filling cements or natural fractures may be altered or overprinted during uplift to the surface and exposure to undersaturated meteoric fluids and associated stress release. A complete understanding of geochemical and geomechanical processes affecting the rocks since their deposition is needed to account for that, otherwise data may not be representative of the subsurface. In this case study using petrographic (point-counting) and petrophysical (porosity and permeability) analyses we highlight the possibilities and limitations of outcrop analog data used for the evaluation of subsurface reservoir quality. The focus is on the Triassic Buntsandstein within the Upper Rhine Graben in southwestern Germany and eastern France and exposed outcrop analogs along the western margin of the graben. Here, we show that some data (detrital composition, quartz cement, K-feldspar cement, and clay mineral cement volumes) may directly be applicable to subsurface reservoir quality assessment. However, other data (porosity, permeability, IGV, carbonate cement, and iron hydroxide cement contents) cannot be used analogously to subsurface samples and we outline possible approaches to mitigate some of the mismatches in the frame of a reservoir quality study. In particular, the correction for uplift diagenetic dissolution of carbonate cemented nodules and goethite precipitation will be the key to gain more accurate results in the presented area.

Depositional Conditions of Cretaceous Ironstones Deposit in the Chulym-Yenisey Basin (Western Siberia)

This study reconstructs the depositional conditions of ironstones within the Chulym-Yenisey basin and assesses the iron source. The detrital minerals of the studied deposits include quartz and feldspar. The authigenic minerals are goethite, siderite, aragonite, dolomite, calcite, apatite, barite, and pyrite. The clay components include minerals of the chlorite group (possible chamosite), nontronite, kaolinite, illite, and beidellite. Local bacterial sulfate reduction led to the formation of pyrite framboids in siltstone layers. The subsequent diagenetic iron reduction promoted the formation of chamosite from siderite. The goethite precipitation occurred in an oxidic aqueous environment. The Cretaceous continental sediments of the Ilek and Kia Formations of the Chulym-Yenisei depression consist of fine- and medium-grained, cross-stratified, poorly sorted litho-feldspatho-quartzose sandstones of fluvial channel origin alternating with bluish-gray siltstones and ironstones of floodplain–lacustrine–bog origin. Thin layers of iron-bearing rocks within siltstones formed in meromictic waters. The changes in geochemical proxies demonstrate fluctuations of paleoenvironmental conditions within the Cretaceous sequence. Siltstones and sandstones formed under humid and arid conditions, respectively. The primary iron source for sediments of the Chulym-Yenisey depression was determined as volcanogenic and igneous rocks of the Altai-Sayan mountainous region.

Comprehensive Utilization of Boron-Concentrate by Hydrometallurgy

A new eco-friendly process to comprehensively utilize boron-concentrate is proposed in this paper. In this process, Iron-concentrate, silicon dioxide, magnesium oxide, and boric acid could be produced from boron-concentrate. The highlight of this process was minimal waste discharge during the whole process. Iron removal was a key step to ensure the quality of boric acid and magnesium oxide. The introduced goethite precipitation method could remove iron to a very low level. With the addition of 3 cm3 H2O2 (5 vol. %) as an oxidizing agent, more than 99% of iron was removed from the leaching liquor. After the removal of iron, the resulting liquor was used to prepare magnesium precipitate. And the optimal preparation conditions were: the temperature of 30 °C and precipitation time of 60 min, ammonium- magnesium ratio of 1.5, the magnesium ion concentration of 34.8 g·L−1. Under those conditions, the magnesium precipitation efficiency was up to 98.5%. Magnesium oxide was obtained by roasting magnesium precipitate at 550 °C for 2 h. Then the mixed crystals of ammonium sulfate and boric acid were obtained by evaporating the liquor after iron removing and magnesium precipitating. Boric acid was separated from ammonium sulfate by dissolving the mixed crystals in ethanol solution.

Genesis of As-Pb-Rich Supergene Mineralization: The Tazalaght and Agoujgal Cu Deposits (Moroccan Anti-Atlas Copperbelt)

Abstract In the Moroccan Anti-Atlas, sulfide deposits hosted by Neoproterozoic to Cambrian formations underwent significant weathering, leading to the formation of supergene profiles. In the Tazalaght Cu-As deposit, three mineralogical steps are distinguished: (1) the replacement of hypogene sulfides (chalcopyrite, pyrite, tennantite) by supergene sulfides (bornite, chalcocite) in the large cementation zone; (2) the formation of oxidized minerals (malachite, azurite, olivenite, and chenevixite, mainly) in a more oxidizing and neutral environment; and (3) the precipitation of goethite, hematite, and quartz in the gossan. In the Cu-As-Pb-V deposit of Agoujgal, the mineralogical units are spatially less confined than at Tazalaght. The narrow cementation zone hosts chalcocite, resulting from the weathering of hypogene chalcopyrite, pyrite, tennantite and galena, while the much more extended and diversified oxidized zone is rich in Cu and Pb carbonates, arsenates, sulfates, phosphates, vanadates, and oxides. Goethite, hematite, mottramite, and late calcite occur in the gossan. Both deposits are characterized by As-rich secondary ores that were formed through similar processes, despite some mineralogical and chemical variations highlighting the influence of the host rocks on weathering. The restricted oxidized mineralization at Tazalaght and the Agoujgal cementation zone most likely arise from the contrasting omnipresence of quartzite at Tazalaght that could not enable a fast and effective neutralization of the fluid’s acidity, and the large amounts of dolomitic host rocks that could be dissolved at Agoujgal. At both sites, the weathering of tennantite through a boxwork texture records the transition from the cementation zone (chalcocite), the oxidized zone (arsenates), and the gossan, and reflects the fluids evolution with time.

Process network modelling of the geochemical reactions responsible for acid mine drainage emanating from the Witwatersrand tailings facilities

ABSTRACTAcid mine drainage (AMD) and associated metal(loid) and SO42- pollution of soil, surface water and groundwater is ubiquitously associated with tailings material generated by Au mining in the Witwatersrand Basin in South Africa. The individual geochemical processes responsible for the AMD generation in this tailings material are relatively well understood. What is less clear are how these different processes interact as a network within the tailings system. Process network modelling (PNM) is a tool that can be used to study such interactive and complex networks of geochemical processes, especially when stochastic methods, e.g. Monte Carlo simulation, are included in the model development. Secondary mineral phase supersaturation requirements from classical nucleation theory are also built into the model.A PNM was developed for a tailings facility in the Witwatersrand gold basin focussing on pH, Fe(total) and SO42- concentrations in the tailings pore water and the relationship of these parameters to the dissolution of pyrite, O2 diffusion into the tailings, oxidation of Fe2+ and the precipitation of secondary minerals, specifically goethite and jarosite. The model indicated that AMD conditions develop fairly rapidly after the sulphidic material is exposed to the Earth’s oxygenated atmosphere. The concentration of H+, and hence the pH, in the tailings pore water is controlled by a number of feedbacks. The positive feedback, implying addition of H+, is the dissolution of pyrite and the precipitation of the secondary Fe3+-bearing minerals goethite and jarosite. Jarosite precipitation was shown to increase the median H+ addition rate by ~2%. The negative feedback, i.e. decrease in H+, is the oxidation of Fe2+ to Fe3+. This feedback loop produces a net excess of H+. Together with the buffer effect of goethite and jarosite precipitation, system steady-state conditions are eventually achieved with respect to pH.The pore water SO42- concentration is controlled by the positive and negative feedback of pyrite dissolution and jarosite precipitation. This feedback loop produces a large excess of SO42- and steady state conditions can only be achieved if SO42- is physically removed from the tailings system, e.g. seepage to groundwater.Oxidation of the Fe2+ produced by pyrite dissolution to Fe3+ is the only positive feedback for tailings pore water Fe3+ concentrations. The negative feedbacks are precipitation of goethite and jarosite and the oxidation of pyrite by Fe3+. The former effect is delayed as these phases first have to achieve a certain level of supersaturation in the tailings pore water solution before they can form. The precipitation of jarosite and goethite, by removing Fe3+ from solution, decreases the effect of Fe3+ pyrite oxidation causing O2 to remain the dominant oxidation mechanism. This feedback loop produces a small excess of Fe3+ over time, however, the model is very sensitive to other factors, e.g. O2 diffusion deeper into the tailings facility.

Hydrogeochemical Investigation of Metal Evolution in Circum-Neutral Mine Discharge

We investigated the removal of metals from a circum-neutral mine discharge over a 0.5-km distance in a series of sequentially interconnected ponds from the exit of an 8-km tunnel that drains a gold mine. The geochemical and mineralogical processes controlling the evolution of metals in the drainage ponds were the focus of this research. We measured the pH and concentrations of dissolved inorganic carbon (DIC) and alkalinity in the aqueous phase and the concentrations of Ca, Mg, Na, Fe, K, Mn, Sr, and Zn in the aqueous phase and in sediments on the beds of the ponds. We calculated the saturated indices of metal oxides, metal carbonates, and the partition coefficients (D) for Mg, Sr, Mn, and Zn. The pH of the mine discharge increased while the concentrations of DIC and alkalinity decreased over the 0.5-km distance. The concentrations of Ca, Mg, Na, Fe, K, Mn, Sr, and Zn generally decreased while their concentrations in the sediment phase increased. Mineralogical and acid-base accounting and modeling results showed that all the metals in equilibrium with the aqueous phase were oversaturated, and the dominant mineral in the precipitated sediments was calcite. Forward geochemical modeling in combination with the Dmg, DSr, DMn, and DZn showed a low ionic strength solution indicating that these metals were removed from the mine discharge by adsorption and coprecipitation of calcites. Forward geochemical modeling results indicated that the groundwater exiting the tunnel had reached equilibrium with respect to ferrihydrite and goethite, suggesting that the precipitation of Fe-oxides were responsible for removing these metals from solution. Calcite precipitation removed about 16% of Ca2+, while 15% of Sr and 5% of Mg were scavenged from the mine water by coprecipitation with calcite and/or adsorption into calcite lattices. About 52% of total Fe from the mine water was scavenged through amorphous Fe(OH)3 and goethite precipitation. About 23% of the Zn in the mine water was removed by sorption on Fe-oxides surfaces or coprecipitation with calcite, and 30% of the Mn in the mine water was removed by rhodochrosite precipitation and/or coprecipitation with calcite. Settling ponds, therefore, provide a framework where minerals precipitate, are adsorbed, or coprecipitated, such that mine water at acceptable contaminant level is released into the natural environment.

Multiobjective-Based Optimization and Control for Iron Removal Process Under Dynamic Environment

Industrial processes often operate in the complex dynamic environment. They challenge the cost-effective and reliable operation of industrial processes. This article proposes a multiobjective optimization and control strategy for the iron removal process to be optimally operated in the dynamic environment. In the optimization layer, multiobjective optimization and local optimization problems, minimizing the process cost and maximizing economic index, are developed to obtain the optimal set-points of the outlet ferrous ion concentrations. In the control layer, model predictive control based on the system dynamic model is constructed to control the outlet ferrous ion concentrations to track the set-points. To reduce the influences from dynamic disturbances and improve the tracking performance, we use least squares support vector machine (LSSVM) to establish the correction model. Fuzzy-logic-based compensation is proposed to compensate the set-points according to the priori and posteriori information. Finally, simulations using real-world plant data are carried out to verify the effectiveness of the proposed control strategy. The simulation results demonstrate that the proposed control strategy achieves a satisfactory tracking performance with less process consumption. It improves the iron content in the goethite precipitate, which has more commercial value. The proposed control strategy can make the plant more profitable.

Reactive alteration of a Mt. Simon Sandstone due to CO2-rich brine displacement

We report a series of acidified brine flow-through experiments designed to quantify the coupled alteration of geochemical, structural and fluid transport properties of a Mt. Simon sandstone core recovered at a depth of 2110.5 m as part of the Illinois Basin Decatur Project (IBDP). Flow-through experiments were completed at representative in-situ conditions to isolate the stages of initial CO2 injection: first, a single-phase (CO2–saturated brine, Stage 1) followed by a second multi-phase (CO2–saturated brine and supercritical CO2, Stage 2) experiment. During both stages, effluent major and trace cation concentrations were tracked through time. Two imaging methods were employed to analyze the structural alterations of the rock core induced by the percolation of CO2-saturated brine and supercritical CO2: (1) scanning electron microscopy-petrography before Stage 1 and after Stage 2 and (2) computed tomography (CT) scans before and after Stage 2.The time series of Stage 1 effluent solutes were used to constrain a reactive transport simulation of the system. Modeling results suggest the evolution of the solute composition is a result of coupled dissolution of K-feldspar, calcite, illite and pyrite, and precipitation of montmorillonite, mesolite, alunite, diaspore, goethite and muscovite. The model predicted a net opening of pore space and associated increased permeability at the inlet. However, across the whole core, an overall decrease in permeability of approximately 23% ± 0.01 after Stage 1 was determined experimentally. CT analysis confirmed a corresponding decrease in porosity. A comparable permeability decrease was directly measured during Stage 2, concurrent with a decrease in the volume of macro-pores based on multiple CT-resolution methods. In total, this coupled approach demonstrates that geochemical alterations exert a first order control on the evolution of fluid transport properties through time at the earliest stages of in-situ CO2 injection and suggest that chemical dynamics ultimately influence both the magnitude and timing of alterations to the physical integrity of Mt. Simon reservoir over these timescales.

Geochemical properties of 40-year old forested pyrrhotite tailings and impact of organic acids on metal cycling

Under humid climate, surface layers of old Cu–Ni pyrrhotite tailings impoundments are typically oxidized and characterized by depletion of sulfides and secondary precipitation of gypsum, jarosite and goethite; metal contaminants are dominantly associated with goethite. In eastern Canada, historical reclamation of such tailings consisted of a period of amendment with lime, fertilizers, and seeding with grass/legume mixtures, followed by forestation. The current study combines characterization of a 40-year old site planted with jack pine and laboratory experiments to evaluate the mineral evolution and the role of organic acids on mineral weathering of oxidized pyrrhotite tailings. In contrast to a nearby control site with no vegetation, gypsum, jarosite and goethite were absent or present in negligible amount in the root-colonized 0–15 cm surface layer of the forested tailings. The results suggested dissolution of the initial secondary minerals with changes in geochemical properties (e.g., increase in pH and organic C content) and pedogenetic processes in the forested tailings. In contrast to the notable loss in total Fe and S from the 0–15 cm layer, Cu and most of the Ni were retained. A 2-month column leaching experiment was conducted to evaluate the impact of repeated additions of low amounts of oxalate, a common organic acid in the rhizosphere, on metal mobilization in oxidized pyrrhotite tailings at pH 2.5, 4 or 6. Gypsum was readily leached regardless of pH or oxalate treatments, whereas jarosite dissolution increased with increasing pH and was further enhanced by the input of oxalate. Indirect evidence of accelerated goethite dissolution by oxalate was provided by the close correlation between dissolved Fe and Cu in oxalate treatment at pH 4 and 6. The oxalate exhibited an increased efficiency in mobilizing Cu as the pH increased. This study emphasizes the contribution of organic acids in metal cycling and their potential impact on the long-term change in Cu and Ni speciation in the root-colonized tailings which may affect metal uptake and migration in the environment.