Gypsum Precipitation Research Articles

Interevaporitic deposits of Las Minas Gypsum Unit: A record of Late Tortonian marine incursions and dolomite precipitation in Las Minas Basin (eastern Betic Cordillera, SE Spain)

The Las Minas Gypsum Unit consists of more than 100 m of alternations of gypsum, carbonates and marls in Las Minas Basin (Betic Cordillera). Although this unit has been previously described as lacustrine, a marine influence in the basin has been suggested. This study provides new geochemical and paleontological data supporting the marine influence during the interevaporitic episodes, allowing to refine the palaeogeography of the eastern Betic Seaway during the Late Tortonian.87Sr/86Sr ratios in gypsum (0.70797 to 0.70825) suggest recycling of Triassic evaporites. The sulphate isotopic values in gypsum (11.5 < δ34SVCDT < 21.9‰; 16.6 < δ18OVSMOW < 28.1‰) are indicative of microbial sulfate-reduction activity. Carbonates are mainly composed of dolomite formed by subspherical crystal aggregates related to bio-mediated processes. The 87Sr/86Sr values in the interevaporitic carbonates (0.70823 to 0.70851) are higher than those expected for Triassic marine authigenic carbonates but lower than expected for the Late Miocene ones, suggesting a mixing of continental and marine water contributions. The ‘non-marine’ isotopic values in gypsum and carbonates contrast with an abundant content of marine siliceous fossils (radiolarians, diatoms, porifera, etc.) in the marls and carbonates that reveals marine incursions into the basin between periods of gypsum precipitation. A tephra layer identified in Las Minas and in the nearby El Cenajo Basin, located in a more inland position, allows a precise correlation between both basins, showing marine fossils in Las Minas and lacustrine in El Cenajo. In El Cenajo Basin, marine microfossils have been found but only in some levels, while others show lacustrine diatoms. A new palaeogeographic model of evaporitic lakes with temporal marine connections is proposed for the latest Tortonian in this region, when the uplift of the Betic Cordillera was very active accelerating the palaeogeographic evolution.

On the retardation mechanisms of citric acid in ettringite-based binders

This study aims to obtain insights into the retardation mechanism of citric acid in an ettringite-based binder from ladle slag and gypsum. The hydration kinetics and phase assemblage of the binder were experimentally investigated and thermodynamically modelled. Additionally, the effects of citric acid on synthetic ettringite were studied to obtain further understanding of the interaction between this organic ligand and the crystal. Experimental results reveal that citric acid works as an inhibitor of ettringite's formation leading to the precipitation of monosulfate and gypsum; the ettringite surface blockage by citrate ligand effectively prevents precipitation of this crystal. This leads to an overestimation in the precipitation of ettringite in the thermodynamic model due to this kinetic barrier imposed by the ligand. Thermodynamic modelling suggests ettringite, monosulfate, aluminum hydroxide, and strätlingite as main hydrates in this binder, whereas an intermixed C–(A–)S–H gel was observed experimentally instead of strätlingite.

Differential Precipitation of Mg(OH)2 from CaSO4·2H2O Using Citrate as Inhibitor-A Promising Concept for Reagent Recovery from MgSO4 Waste Streams.

In hydrometallurgical processing and acidic wastewater treatment, one of the neutralizing agents employed is MgO or Mg(OH)2. At the end of this process, the resulting solution, which is rich in SO42− and Mg2+ is treated with lime to remove (or minimize the amount) of these ions via the precipitation of Mg(OH)2 and CaSO4·2H2O (gypsum). In our work, an attempt was made to separate the two solids by increasing the induction time of the gypsum precipitation, thus regenerating relatively pure Mg(OH)2 which could be reused in wastewater treatments or hydrometallurgical processing circuits, and in this way, significantly enhancing the economic viability of the process. During our experiments, the reaction of an MgSO4 solution with milk of lime prepared from quicklime was studied. The effects of a range of organic additives, which can slow down the precipitation of gypsum have been assessed. The process was optimized for the most promising inhibiting agent—that is, the citrate ion. The reactions were continuously monitored in situ by conductometric measurements with parallel monitoring of solution pH and temperature. ICP-OES measurements were also carried out on samples taken from the reaction slurry. The composition of the precipitating solids at different reaction times was established by powder XRD and their morphology by SEM. Finally, experiments were carried out to locate the additive after the completion of the precipitation reaction to get information about its potential reuse.

Chemical Treatment of Highly Toxic Acid Mine Drainage at A Gold Mining Site in Southwestern Siberia, Russia

The critical environmental situation in the region of southwestern Siberia (Komsomolsk settlement, Kemerovo region) is the result of the intentional displacement of mine tailings with high sulfide concentrations. During storage, ponds of acidic water with incredibly high arsenic (up to 4 g/L) and metals formed on the tailings. The application of chemical methods to treat these extremely toxic waters is implemented: milk of lime Ca(OH)2, sodium sulfide Na2S, and sodium hydroxide NaOH. Field experiments were carried out by sequential adding pre-weighed reagents to the solutions with control of the physicochemical parameters and element concentrations for each solution/reagent ratio. In the experiment with Ca(OH)2, the pH increased to neutral values most slowly, which is contrary to the results from the experiment with NaOH. When neutralizing solutions with NaOH, arsenic-containing phases are formed most actively, arsenate chalcophyllite Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O, a hydrated iron arsenate scorodite, kaatialaite FeAs3O9·8H2O and Mg(H2AsO4)2. A common specificity of the neutralization processes is the rapid precipitation of Fe hydroxides and gypsum, then the reverse release of pollutants under alkaline conditions. The chemistry of the processes is described using thermodynamic modeling. The main species of arsenic in the solutions are iron-arsenate complexes; at the end of the experiments with Ca(OH)2, Na2S, and NaOH, the main species of arsenic is CaAsO4−, the most toxic acid H3AsO3 and AsO43−, respectively. It is recommended that full-scale experiments should use NaOH in the first stages and then Ca(OH)2 for the subsequent neutralization.

Mineral Recovery Enhanced Desalination (MRED) process: An innovative technology for desalinating hard brackish water

Desalination of water containing high concentrations of calcium, dissolved carbon dioxide, sulfate, silica and other sparingly soluble salts is difficult because of the scaling potential. An innovative pre-treatment scheme was investigated at bench scale that selectively removes these constituents and produces a soft water to enable desalination with high feed water recovery. The process first removes dissolved carbon dioxide by air stripping at low pH. Magnesium is removed by precipitation at high pH. Calcium is removed by ion exchange (IX), and sulfate is removed by nanofiltration (NF). Cation regenerant from IX, containing calcium, and concentrate from NF, containing sulfate, is combined to precipitate gypsum. Concentrate from the desalination process consisting of a concentrated NaCl solution is used to regenerate the IX resins. The selective precipitation, IX, and NF processes were tested in laboratory experiments and produced magnesium hydroxide and gypsum at greater than 90% and 95% purity respectively. A process model was developed to calculate process performance, mass and liquid flow rates. The MRED process offers the following benefits: 1) greater recovery of brackish feedwater by a desalination process, 2) recovery of marketable commodities and 3) reduction in the volume and mass of waste products from the treatment process.

Sulfate Resistance in Cements Bearing Ornamental Granite Industry Sludge.

This study explores the effect on sulfate resistance of the use of ornamental granite industry waste as a supplementary cementitious material (at replacement ratios of 10% and 20%) in cement manufacture. The present paucity of scientific knowledge of the behaviour of these new cements when exposed to an external source of sulfates justifies the need for, and the originality of, this research. After characterising the waste chemically and mineralogically, cement paste specimens were prepared in order to determine the durability of the newly designed eco-cements using Köch–Steinegger corrosion indices. The new hydration products, which might induce microstructural, mineralogical, or morphological decay in the specimens, were also analysed by comparing the samples before and after soaking in a sodium sulfate solution for different test periods. Respect to the results, the damage to pastes bearing 10% granite sludge (GS) is the same as observed in OPC, whilst the former exhibit a higher Köch-Steinegger corrosion rate (1.61) than both OPC and OPC+20GS. Soaking the pastes in sodium sulfate induces matrix densification due to ettringite formation and gypsum precipitation in the pores. Further to those results, at an optimal replacement ratio of 10%, these alternative, eco-friendlier materials can be used in the design and construction of non-structural cement-based (mortar or concrete) members exposed to an external source of sulfate.

Chemical evolution and evaporation of shallow groundwaters discharging from a gold mine, southern New Zealand

Waste rock piles at the Macraes gold mine in southern New Zealand expose abundant fresh schist to alteration reactions that principally involve pyrite, chlorite, and calcite, yielding alkaline waters (pH~8) with elevated dissolved loads. Pyrite oxidation has resulted in dissolved sulfate concentrations rising up to ~3000 mg/L over 10 years, and this high sulfate is a potential environmental issue in waters leaving the site. Up to 600 mg/L dissolved Mg2+ results from chlorite dissolution. The site has a semi-arid climate and evaporative precipitation of sulfate minerals could contribute to an engineered water treatment system. However, the evolved waters are saturated or supersaturated with respect to carbonate minerals and spontaneous precipitation of aragonite is widespread, thereby limiting Ca-sulfate (gypsum) precipitation. Localised precipitation of Mg-sulfate (epsomite) also occurs, but this redissolves during rain events. Compositionally different waters seeping from the mine tailings impoundment have >2500 mg/L dissolved sulfate, and elevated Na+, K+ and Cl− from addition of reagents in the processing system. These seepage waters have also undergone interaction with waste rocks in the impoundment walls. The seep waters are approximately saturated with respect to carbonate minerals, but no spontaneous carbonate precipitation has occurred over two years of observations. Ephemeral evaporative epsomite and Na–Mg sulfate (bloedite) precipitates form locally. Geochemical modelling suggests that evaporative precipitation of gypsum has potential to remove sulfate from both types of water, especially if carbonate precipitation was suppressed by lowering the water pH to ~6 in an engineered treatment system that involves substantial evaporation.

The effect of phosphonate-based antiscalant on gypsum precipitation kinetics and habit in hyper-saline solutions: An experimental and modeling approach to the planned Red Sea – Dead Sea Project

The effect of phosphonate-based antiscalant on the precipitation kinetics of gypsum under the hyper-saline solutions relevant to the Red Sea-Dead Sea desalination project was studied. Batch experiments were carried out to determine the effect on the induction times and rates of nucleation and gypsum crystal growth. A wide range of ionic strength (5.5–9 m), pH (6.33–6.91) and oversaturation with respect to the mineral (1.69 ≤ Ωgypsum ≤ 2.11) were covered in the experiments.Induction times in solutions that contained the antiscalant were longer by about 20–500% compared to solutions with a similar composition that did not contain the antiscalant. In the presence of the antiscalant fewer crystals precipitated that were larger in size. The specific surface area of the crystals that precipitated in solutions that contained the antiscalant were smaller in about 20–500% than those that precipitated in solutions that did not contain the antiscalant, and the relative specific surface area was in agreement with the induction time. We conclude that increased interfacial tension in the presence of the antiscalant, retards nucleation and reduces the surface area available for growth. Subsequent rates of crystal growth were impervious to the presence of the antiscalant.

The kinetics of the precipitation of gypsum, CaSO4·2H2O, over a wide range of reactant concentrations

In this work, the precipitation kinetics of gypsum was studied over a wide range of degree of supersaturation at 25 °C in the reaction $${\text{Na}}_{2} {\text{SO}}_{{4\left( {{\text{aq}}} \right)}} + {\text{CaCl}}_{{2\left( {{\text{aq}}} \right)}} + 2{\text{ H}}_{2} {\text{O}} \to 2{\text{ NaCl}}_{{\left( {{\text{aq}}} \right)}} + {\text{CaSO}}_{4} \cdot 2{\text{ H}}_{2} {\text{O}}_{{\left( {\text{S}} \right)}}$$ with the aim of constructing a comprehensive kinetic model for CaSO4·2H2O(s) formation that is valid from the lowest (0.04 M) to the highest (0.20 M) feasible initial reactant concentration. To monitor the variation of reactant concentrations during the precipitation reaction, conductometry was employed. For reasonably slow reactions (where the establishment of the equilibrium potential on the indicator electrode was possible), the measurements were supplemented by a Ca-ion-selective electrode. The structure and morphology of the precipitating solids was characterized by XRD and SEM. The induction period was found to decrease about two orders of magnitude with the increasing reactant concentration. It was experimentally established that the influence of the so-called wall effect is of secondary importance. Using the data collected, a kinetic model have been suggested that can describe the entire precipitation process of gypsum simultaneously, incorporating nucleation and crystal growth, in a wide concentration range. Our calculations strongly suggest that the inclusion of the CaSO4(aq) ion pair is necessary for the appropriate kinetic description of gypsum precipitation.

Effect of Fe2+ ions on gypsum precipitation during bulk crystallization of reverse osmosis concentrates

In reverse osmosis desalination, the concentrate is a saline solution that may become supersaturated. Heterogeneous nucleation of salts occurs at the membrane surface, resulting in the buildup of inorganic deposits on the membrane. The inorganic nucleation process, however, is complex in natural waters. Most studies focused primarily on single salt fouling of membranes, and related treatment for single solute systems. However, scale formation, especially gypsum, is affected by the presence of different salts and metals. In this wok, for the first time, we investigate the mixed precipitation of iron oxides and gypsum. The role of citric acid in the inhibition of precipitation was studied for different concentrations in both the absence and the presence of Fe2+. Conductivity and ion concentration measurements were used to estimate the formation time of gypsum. Scanning electron microscopy, X-Ray Diffraction (XDR) analysis, and Infra-Red spectroscopy analysis were used to provide structural information. Collected data showed that the presence of Fe2+ accelerates gypsum precipitation and shortens its induction time. Analytic results showed that gypsum crystals are greatly affected by the presence of Fe2+ ions, which generated needle shaped crystals. Citric acid can delay the induction time of gypsum precipitation. It also affects the morphology of gypsum crystals through adsorption mechanism. XDR diagrams revealed that the presence of citric acid (20 mg/L) can stabilize the bassanite phase (CaSO4·½H2O) for much longer periods. In the presence of Fe2+ ions, citric acid extends the induction time of calcium sulfate and minimizes the acceleration effect of Fe2+ ions. SEM images showed that the presence of ferrous ions during the chemical inhibition generates the β-hemihydrate form of calcium sulfate.

Revised chronology of the ICDP Dead Sea deep drill core relates drier-wetter-drier climate cycles to insolation over the past 220 kyr

The Dead Sea Deep Drilling Project drilled 456 meters into the deepest floor of the Dead Sea and recovered a record of the past ∼220 kyr of the Levant hydroclimate history, that is, Marine Isotope Stages 1–7, including the last three interglacials and the last two glacials. We present an updated chronology of the core from DSDDP Hole 5017-1-A, from the Dead Sea’s deepest basin, that refines our previous chronology (Torfstein et al. 2015) based on new information. The updated chronology uses the following approaches: (1) radiocarbon ages of Kitagawa et al. (2017); (2) correlation of specific layers in the core with U–Th-dated sediments on the Dead Sea margin, particularly during the interval of glacial Lake Lisan (MIS 2,3,4); (3) tuning of the δ18O data of DSDDP core aragonite to the U–Th dated oxygen isotopes of regional cave speleothems; and (4) tuning of the DSDDP aragonite δ18O data to summer insolation curves when the cave δ18O chronology is less clear. The updated chronology reveals a strong relationship between the sedimentary facies comprising the core and Northern Hemisphere summer insolation variations. It shows that sequences of sediments marking drier/wetter/drier climate conditions in the lake’s watershed (e.g., salt/muds/salt, respectively) appear across the flank/peak/flank segments of several summer insolation peaks. In particular, the transition from drier to wetter sedimentary facies during mid-latitude insolation peaks coincides with the intervals of sapropel conditions in the Mediterranean, reflecting enhanced Nile flow due to intense African monsoonal conditions, and marking the impact of the tropical precession cycles on Eastern Mediterranean hydroclimate. This pattern was lost during MIS 2,3,4, when mostly sequences of primary aragonite are punctuated by gypsum precipitation during Heinrich events, marking the strong impact of the North Atlantic on the last glacial Levant hydroclimate.

Implications of microbial mat induced sedimentary structures (MISS) in carbonate rocks: An insight from Proterozoic Rohtas Limestone and Bhander Limestone, India

A variety of microbial mat induced sedimentary structures (MISS) occur in the basal part of the Mesoproterozoic Rohtas Limestone and the Bhander Limestone, India. The combined outcrop and petrographic studies establish unicellular microbial origin of the MISS in the Rohtas Limestone and the Bhander Limestone. Micro-scale deformations associated with MISS imply the late cementation. Paradoxically MISS, once formed, has a better preservation potential in carbonate sediments because of their proneness to get cemented early. The studied basal sections of both the formations built up in a low energy depositional condition. In warm and arid tropical climate, high concentration of dissolved inorganic carbon exacerbated precipitation of aragonite crystals in successive stacks and sulfur concentration led to gypsum precipitation. However, the temperature in the palaeodepositional environment could have been high enough to restrict the sulfur reduction rate severely hampering the growth of sulphur reducing bacteria (SRB) population which was the most powerful post-Archaean calcification engine. The available results indicate Mesoproterozoic palaeotemperature raised up to 32°C at a mid-latitude location. In the Vindhyan sea straddling across the equator, temperature is predicted to have been considerably higher. The ancient marine limestone formations having MISS, irrespective of their age, developed in similar low palaeolatitudinal locations. Thus, it is reasonable to attribute that high temperature at depositional site cards carbonate sediments to acquire MISS by delayed cementation. Early cementation hinders MISS formation in carbonate sediments, till the sea water temperature crosses an optimal value.

Mobility of REE from a hyperacid brine to secondary minerals precipitated in a volcanic hydrothermal system: Kawah Ijen crater lake (Java, Indonesia)

Rare Earth Elements (REE; lanthanides and yttrium) are elements with high economic interest because they are critical elements for modern technologies. This study mainly focuses on the geochemical behavior of REE in hyperacid sulphate brines in volcanic-hydrothermal systems, where the precipitation of sulphate minerals occurs. Kawah Ijen lake, a hyperacid brine hosted in the Ijen caldera (Indonesia), was used as natural laboratory. ∑REE concentration in the lake water is high, ranging from 5.86 to 6.52 mg kg−1. The REE pattern of lake waters normalized to the average local volcanic rock is flat, suggesting isochemical dissolution. Minerals spontaneously precipitated in laboratory at 25 °C from water samples of Kawah Ijen were identified by XRD as gypsum. Microprobe analyses and the chemical composition of major constituents allow to identify possible other minerals precipitated: jarosite, Al-sulphate and Sr, Ba-sulphate. ∑REE concentration in minerals precipitated (mainly gypsum) range from 59.53 to 78.64 mg kg−1. The REE patterns of minerals precipitated normalized to the average local magmatic rock show enrichment in LREE. The REE distribution coefficient (KD), obtained from a ratio of its concentration in the minerals precipitated (mainly gypsum) and the lake water, shows higher values for LREE than HREE. KD-LREE/KD-HREE increases in the studied samples when the concentrations of BaO, MgO, Fe2O3, Al2O3, Na2O and the sum of total oxides (except SO3 and CaO) decrease in the solid phase. The presence of secondary minerals different than gypsum can be the cause of the distribution coefficient variations.High concentrations of REE in Kawah Ijen volcanic lake have to enhance the interest on these environments as possible REE reservoir, stimulating future investigations. The comparison of the KD calculated for REE after mineral precipitation (mainly gypsum) from Kawah Ijen and Poás hyperacid volcanic lakes allow to generalize that the gypsum precipitation removes the LREE from water.

A novel approach for treating acid mine drainage through forming schwertmannite driven by a mixed culture of Acidiphilium multivorum and Acidithiobacillus ferrooxidans prior to lime neutralization

As the predominant treatment approach of acid mine drainage (AMD), lime neutralization often exhibits inefficiencies since the abundance of iron and sulfate in AMD usually form iron hydroxide and gypsum precipitate coatings on the surface of lime. In this study, a novel approach of biomineralization prior to lime neutralization for treating AMD was proposed, in which iron and sulfate were biologically precipitated as schwertmannite through iron biological reduction-oxidation driven by a culture mixed with Acidiphilium multivorum JZ-6 and Acidithiobacillus ferrooxidans LX5. It was found that only five cycles of iron reduction by A. multivorum JZ-6 followed by iron oxidation by A. ferrooxidans LX5 could remove completely iron and nearly 40% of sulfate in AMD, while non-ferrous metals (Al, Mn, Cu, Ni, and Zn) were hardly removed. Consequently, the amounts of lime required and sludge generated in the subsequent lime neutralization process were reduced by 56% and 68%, respectively. As a result, the content of non-ferrous metals in the sludge was increased by 3.2 folds. The level of Al was increased surprisingly to 19% (wt/wt), a level similar to the commercially valuable bauxite. The novel process of biomineralization prior to lime neutralization provides a sustainable way for AMD treatment.

Carbonate laminae recorded in a siliciclastic tidal flat colonized by microbial mats

Microbial mats in siliciclastic coastal environments are considered as non-lithifying systems that lack the potential for calcification. This work documents precipitation and preservation of well-defined, laterally continuous carbonate laminae in low-relief microbial mats from a siliciclastic supratidal flat in northern Patagonia (Paso Seco, Argentina). Petrographic, epifluorescence, and SEM-EDS studies of surficial and buried microbial mats show that they are composed of repeated sediment sequences comprised of four different types of laminae, which are, from base to top: (A) a sand and silt lamina, (B) a lamina largely composed of organic matter displaying moulds of subvertical cyanobacteria filaments, (C) a lamina composed of dense micritic carbonate, which is cut by moulds of vertical cyanobacteria filaments, and (D) a lamina composed of organic matter containing abundant horizontal cyanobacteria filaments. The formation of each different lamina is strongly controlled by the environmental conditions, characterized by episodic seawater flooding, followed by several days to weeks in which water remains covering the sediment and gradually evaporates producing a salinity increase and the precipitation of calcite, gypsum and halite. Thus, the basal sand and silt lamina forms as the result of the transport of siliciclastic grains and particles during seawater flooding. The overlying lamina B, composed of organic matter with moulds of subvertical cyanobacteria filaments, is formed when calm water conditions are recovered and organic material is produced by photosynthetic microbial activity. The following lamina C, composed of dense micritic carbonate, precipitates when the salinity of stagnant water reaches CaCO3 supersaturation. Finally, the uppermost lamina D, composed of organic matter with horizontal cyanobacteria filaments, is developed while the sediment surface is drying and gypsum and halite precipitate, although these minerals are not preserved in the sediment because they dissolve during subsequent inundations. All these observations show that well-developed, laterally-continuous carbonate laminae may be formed and preserved in a siliciclastic tidal environment if biotic and abiotic sedimentary processes closely interact to create the required conditions. The studied microbial mats increase sediment impermeability, which favours water retention in the flat and, thus, subsequent evaporation of the retained seawater. Moreover, microbial cells and EPS (extracellular polymeric substance) suspended in seawater might act as nuclei for CaCO3 precipitation, which will later settle down on the microbial mat. In addition, EPS of the microbial mats may also serve as nucleus for in situ carbonate precipitation.

Verhalten von Sulfatgestein im Tunnelbau – Erfahrungen aus Feldbeobachtungen und In‐situ‐Quelldrücke

AbstractTunnels and underground works in sulphate bearing rocks are very challenging. For more than a century experience has accumulated in Switzerland and southern Germany with difficult conditions during construction and operation, which show the difficult conditions with extreme, long lasting heave of the invert and extreme swelling pressures. The analyses of published experience over more than a century and recent personal experience led to the compilation of many pieces of a puzzle and to a better understanding of complex processes. The swelling processes in sulphate bearing rocks are triggered by the formation of flow path for water, the dissolution, concentration and precipitation of minerals. In particular Anhydrite is dissolved and the solution becomes saturated, until precipitation and crystallization of Gypsum starts. The applied construction methods play an important influence on the rock mechanics and geochemical processes and finally the magnitude of in‐situ swelling pressures. The in‐situ swelling pressure are still large, but substantially less than the swelling pressures from laboratory tests. Estimated swelling pressures will be indicated.

Origin and depositional paleoenvironment of Triassic polyhalite in the Jialingjiang Formation, Sichuan Basin

The Sichuan Basin contains the most prolific marine potash salt deposits in China. Although a vast amount of polyhalite has been found in the Triassic Jialingjiang Formation, the production of soluble potash deposits has yet to begin. The origin and sedimentary environment of polyhalite has remained unclear, and this information could have a significant economic impact. The recent discovery of protogenetic polyhalite co-existing with halite crystals in cores from the early Triassic Jialingjiang Formation in eastern Sichuan Basin provides vital clues to its origin and depositional environment. Two types of polyhalite have been identified, through the examination of sedimentary textures and fabrics, mineral composition and contents, and major and trace elements from cores. The first type is protogenetic polyhalite, which co-exists and is commingled with halite crystals. The second type is secondary in origin with a radiating texture and was formed by the metasomatism of gypsum. Triassic polyhalite and halite was deposited during periods of freshwater and sylvite-saturated, evaporated seawater mixing. Further dilution of the freshwater resulted in gypsum precipitation among the halite crystals. After periods of desalination, increasing evaporation leads to the formation of highly concentrated and dense brines that are rich in potassium and magnesium. These heavy brines sink downward through intercrystalline pores and fractures, replacing gypsum with polyhalite through metasomatism. These sequential phenomena occur because the Triassic marine basins were relatively small and tectonically active. Although these shallow, small salt basins can have a fast concentration rate, they can be easily desalinated by the peripheral freshwater input in an overall arid but fluctuating arid and wet climate. The alternating periods of evaporation and desalination are responsible for the formation of soluble potassium salt deposits. Our proposed mechanisms provide useful information for understanding the distribution of polyhalite. These mechanisms can be used to guide future exploration and production of Triassic marine potash salts in the periphery of the Tethys Ocean.

Remediation by waste marble powder and lime of jarosite-rich sediments from Portman Bay (Spain)

We investigate the use of hydrated lime and calcite waste marble powder as remediation treatments of contaminated jarosite-rich sediments from Portman Bay (SE, Spain), one of the most contaminated points in the Mediterranean coast by mining-metallurgical activities. We tested two commercial hydrated limes with different Ca(OH)2 percentages (28 and 60% for Lime-1 and Lime-2 respectively) and two different waste marble powder, WMP, from the marble industry (60 and 96% of calcite for WMP-1 and WMP-2 respectively). Mixture and column experiments and modelling of geochemical reactions using PHREEQC were performed. Lime caused the precipitation of hematite, gypsum and calcite, whereas WMP treatments formed iron carbonates and hematite. The fraction of amorphous phases was mainly composed of iron oxides, hydroxides and oxyhydroxides that was notably higher in the lime treatment in comparison to the WMP treatment. The reactive surface area showed a positive trend with the amorphous phase concentration. Results highlighted the effectiveness of lime treatments, where Lime-2 showed a complete elimination of jarosite. Column experiments revealed a clear reduction of heavy metal concentration in the lixiviate for the treated sediments compared to the original sediments. Particularly, Lime-2 showed the highest reduction in the peak concentration of Fe, Mn, Zn and Cd. The studied treatments limited the stabilisation of Cr and Ni, whereas contrarily As increases in the treated sediment. PHREEQC calculations showed that the most concentrated heavy metals (Zn and Mn) are stabilized mainly by precipitation whereas Cu, Pb and Cd by a combination of precipitation and sorption processes. This chemical environment leads to the precipitation of stable iron phases, which sorb and co-precipitate considerable amounts of potentially toxic elements. Lime is significantly more effective than WMP, although it is recommended that the pH value of the mixture should remain below 9 due to the amphoteric behaviour of heavy metals.

Using the composition of fluid seepage from the magmatic-hydrothermal system of Kawah Ijen volcano, Indonesia, as a monitoring tool

The lake waters of Kawah Ijen volcano are concentrated hyperacidic brines that obtain their composition from volcanic gases and water-rock interaction. Lake water and hydrothermal fluids seep through the western flank of the volcano where they precipitate gypsum and form the hyperacid Banyu Pahit river. In this contribution, we present compositional data from bi-weekly samples taken from the Banyu Pahit between 2015 and 2018 to evaluate whether these fluids can be used to monitor the hydrothermal system, and compare the fluids to the record of variability documented by the precipitated gypsum. Understanding the causal links between variability of the Banyu Pahit and the magmatic-hydrothermal processes operating in the Kawah Ijen system, and establishing a baseline for quiescence are pre-requisites to using the river for monitoring. Fluid samples were analysed at the Ijen observatory for SO4/Cl ratio using BaSO4 turbidity and AgCl gravimetry, and subsequently sent for ICP-MS and ICP-OES analyses. The data shows a first order seasonal variation that can be explained by variable input of neutral groundwater, but is underlain by more subtle trends. Temporally, there is a shift in the system from 2015–2016 to 2017 when the fluid contains a higher proportion of elements derived from rock alteration. The shift occurs at the peak of the rainy season and coincides with a substantial rainfall increase in 2017 compared to 2015–2016. At the start of 2018 there is a marked increase in Cu, coinciding with a gas burst in March 2018. We suggest that an increased meteoric water input led to an increase in water-rock interaction and dissolution of a Cu-sulphide phase in the hydrothermal system. The variability of the fluids over the 3-year sampling period does not exceed that of the longer record preserved by the gypsum precipitates, indicating that it is typical for the current style of activity.

Effect of various metal ions on gypsum precipitation

ABSTRACT The effect of various metal ions, namely Mn2+, Al3+, Pb2+, Cr3+, and Zn2+, on the precipitation of gypsum was investigated in the present study. The structure, functional groups, morphology, and size of gypsum crystals precipitated with additives using the batch method were evaluated experimentally through X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA)-Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and particle size and morphological analysis. The results indicate that Pb2+ and Zn2+ ions, in particular, exerted significant effects on gypsum precipitation. When Al3+ ions were the additive, only needle-like gypsum formed, whereas compact plate-like gypsum was observed in the presence of Pb2+ ions. The addition of Zn2+ ions resulted in gypsum particles of larger sizes with agglomerated shapes, simultaneously achieving an increased filtration rate of the suspensions from 5.88×10−7–2.44 × 10−6 m3/s. A detailed analysis of the crystal shape showed that while the elongation values decreased, the circularity values increased as compared with the gypsum precipitated in pure medium. These results show how metal ions can be used to effectively modify gypsum size, shape, and crystal morphology.