Secondary Salt Research Articles

Exploring salinity origins in the Ghiss-Nekor aquifer, northern Morocco: A multivariate statistical analysis

The Ghiss-Nekor coastal aquifer is characterized by high salinity stemming from multiple sources, remains poorly investigated. This study aims to address this knowledge gap by employing both univariate (descriptive statistics) and multivariate statistical analyses, including correlation matrix and principal component analysis (PCA). Groundwater samples were collected from 52 sites across the study area and meticulously analyzed for pH, TDS, EC, and the ions such as Na+, K+, Mg2+, Ca2+, NH4+, HCO3-, NO3-, NO2-,Cl-, SO42-, PO43-, and SiO2. Descriptive statistics, notably standard deviation (SD), highlight the diverse sources contributing to salinization, among which seawater intrusion (SWI) emerges as a significant factor. Correlation matrix analysis underscores multiple pathways for salinization, implicating SWI, salt dissolution, chemical weathering, secondary salt leaching, and anthropogenic activities. PCA elucidates 81.05% of the total variance in physicochemical parameters, with strong loadings observed for EC, Na+, Cl-, and Mg2+, corroborating the influence of SWI and suggesting evaporation processes. Moreover, PCA reinforces the potential influence of both geogenic and anthropogenic factors in salinization within the study area. This comprehensive investigation provides valuable insights into the elevated salinity levels observed in the Ghiss-Nekor aquifer, contributing to a deeper understanding of its hydrogeochemical dynamics.

A systematic deliquescent additive selection approach for enhancement of reaction kinetics of thermochemical heat storage materials

A series of 16 salt mixtures consisting of potassium carbonate (K2CO3) as the base salt and a secondary salt hydrate in a 20 : 1 mol ratio of anhydrous K2CO3 to anhydrous additive were investigated as potential thermochemical heat storage (TCHS) composites. Those materials were evaluated based on their (de)hydration temperatures and reaction kinetics to find a suitable secondary salt mixture with enhanced phase change behaviour. The improved performance is expected to come from the enhancement of ionic mobility due to the deliquescence of the secondary salt. Based on the screening, we found that deliquescent and highly soluble salts are prone to reacting with K2CO3, forming new compounds that do not impact the behaviour of the base salt. Therefore, the most promising additives were salts that share a common ion with K2CO3 (KF, Cs2CO3) or salts that can react with K2CO3 forming a highly deliquescent salt (CsF, Cs2SO4). Based on the findings, we were able to design a selection procedure that can be applied to other salt hydrates considered for TCHS applications that suffer from poor kinetics and large reaction hysteresis.

Upscaled Synthesis Protocol for Phase-Pure, Colloidally Stable MXenes with Long Shelf Lives.

MXenes are electrically conductive 2D transition metal carbides/nitrides obtained by the etching of nanolaminated MAX phase compounds, followed by exfoliation to single- or few-layered nanosheets. The mainstream chemical etching processes have evolved from pure hydrofluoric acid (HF) etching into the innovative "minimally intensive layer delamination" (MILD) route. Despite their current popularity and remarkable application potential, the scalability of MILD-produced MXenes remains unproven, excluding MXenes from industrial applications. This work proposes a "next-generation MILD" (NGMILD) synthesis protocol for phase-pure, colloidally stable MXenes that withstand long periods of dry storage. NGMILD incorporates the synergistic effects of a secondary salt, a richer lithium (Li) environment, and iterative alcohol-based washing to achieve high-purity MXenes, while improving etching efficiency, intercalation, and shelf life. Moreover, NGMILD comprises a sulfuric acid (H2 SO4 ) post-treatment for the selective removal of the Li3 AlF6 impurity that commonly persists in MILD-produced MXenes. This work demonstrates the upscaled NGMILD synthesis of (50g) phase-pure Ti3 C2 Tz MXene clays with high extraction yields (>22%) of supernatant dispersions. Finally, NGMILD-produced MXene clays dry-stored for six months under ambient conditions experience minimal degradation, while retaining excellent redispersibility. Overall, the NGMILD protocol is a leap forward toward the industrial production of MXenes and their subsequent market deployment.

Diagnosis of Groundwater Quality in North Assiut Province, Egypt, for Drinking and Irrigation Uses by Applying Multivariate Statistics and Hydrochemical Methods

Globally, groundwater is a valuable natural resource that may be relied upon for irrigation and drinking needs. The main purpose of this study is to investigate the groundwater geochemistry in the West of El Qusiya, Assuit, Egypt. Groundwater suitability for irrigation has been estimated with some methods, for instance, electrical conductivity (EC), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Killey ratio (KR), magnesium hazard (MH), permeability index (PI), Piper trilinear diagram, and USSL diagram. The Piper diagram shows that the sodium and potassium (Na+K) kind dominates the water chemistry, followed by the mixed type. The principal coordinate analysis (PCoA), cluster analysis (CA), principal component analysis (PCA), and Pearson correlation matrix analysis (PCMA) statistical methods reveal that the physicochemical parameters of water collected from the Eocene and Pleistocene aquifers are produced from mixed origins. The geogenic origin reflects the lithologic impact of aquifers matrix and water interactions, in addition to anthropogenic sources caused by infiltration of secondary salts initiated due to fertilizers and agriculture water. These factors are the controller for groundwater’s ionic (Na+, Ca2+, Mg2+, K+, Cl−, SO42−, and HCO3−) variation in the area studied. Based on SAR, KR, and PI results, groundwater is acceptable for irrigation. Consistent with RSC, MH, and Na% results, approximately 50% of the groundwater samples are unsuitable for irrigation use.

Geochemical evaluation of groundwater around Chromepet tannery belt, Southern India

The study appraises the geogenic and anthropogenic contamination of groundwater around tanneries located in Chromepet, Southern India. Thirty-six groundwater samples were examined for major anions, cations and trace metals concentration. The concentration of chromium (Cr), iron (Fe) and lead (Pb) in the study area ranges from 0.04 to 0.51 mg/L, 0.001–1.07 mg/L and 0.001–0.09 mg/L respectively. 97% of the samples exceeded the acceptable range for Cr whereas, lead and iron exceeded 89 and 8% of the samples respectively. The high concentrations of chromium, iron and lead in the groundwater are due to the influence of tannery effluents. The majority of the samples in the study area suggested silicate weathering. The piper plot reveals that 50% of the water samples have Na–Cl type water which is possibly due to anthropogenic sources. The Chadha plot revealed that silicate weathering and ion exchange govern the bulk of groundwater chemistry in freshwater aquifers owing to carbonate precipitation and mineral dissolution. Durov plot highlights that the bulk of the samples has no dominating anion or cation types, indicating simple dissolution or mixing. Saturation Index (SI) reveals that 50% of the samples were supersaturated due to calcite and dolomite precipitation. Principal Component Analysis (PCA) 1 suggested secondary salt discharge from geogenic and anthropogenic processes due to tanning industries. Increasing the performance of wastewater treatment plants is essential to improve the groundwater quality of the region under tannery influence.

Conversion rules of sulfur compounds in iron chelate desulfurization system

ABSTRACT Iron chelate desulfurization is a popular method in the coking industry due to its low generation of secondary salts. The conversion of sulfur compounds in the system plays a crucial role in this process. In this paper, the favorable conditions for the formation of polysulfide ions (Sx 2-) were investigated by ultraviolet-visible spectrophotometry (UV-Vis) in the reaction system of EDTA-Fe and Na2S. The reaction solution was analyzed by high-performance liquid chromatography (HPLC), aiming to obtain the main forms of the presence of Sx 2- after the reaction. HS− was first converted to Sx 2-, and then to elemental sulfur (S8). In the experimental range, the concentration of Sx 2- increased with increasing the concentration ratio of reactants (c(Na2S)/c(EDTA-Fe)) and decreasing the temperature, was maximal at pH 9.84. At c(Na2S)/c(EDTA-Fe) of 120, the forms of Sx 2- reached a maximum, which was S3 2--S10 2-. When the concentration ratio reached 130, S8 was generated, as the concentration ratio increased on this basis, the time for S8 to appear was shortened from 21 min to 12 min. Therefore, the study of the conversion rules of sulfur compounds in the iron chelate desulfurization system provides both the ideas to suppress the generation of by-salts in this system and new evidence to reveal the common problem of sulfur compounds conversion in the wet catalytic oxidation desulfurization process.

Spectrophotometric Determination of Thiosulfate in Desulfurization Solutions by Decoloration of Methylene Blue

Spectrophotometric Determination of Thiosulfate in Desulfurization Solutions by Decoloration of Methylene Blue Published on: May 1, 2023 Xiuxiu Zhao, Ming Xu, Chunying Ma, Yingying Ma, Xianji Ma Spectroscopy, May 2023, Volume 38, Issue 5 Pages: 19–22,34 This article proposes a method for the determination of thiosulfate by decoloring spectrophotometry with methylene blue as an oxidant. Methylene blue has redox properties. Its oxidized form is blue, and its reduced form is colorless. Thiosulfate is a medium-strength reducing agent. In an acidic medium, the two can undergo redox reactions to reduce methylene blue and cause the solution to exhibit a fading reaction within a certain range, and the degree of fading is proportional to the amount of thiosulfate added. This method measures the change in absorbance (AU) at a fixed wavelength of 664 nm, and ΔAU has a linear relationship with the content of thiosulfate. The linear range is 0–0.3 mmol/L. From this curve, the content of thiosulfate in the desulfurization solution can be accurately measured. This method is not interfered with by other secondary salts in the desulfurization solution during the thiosulfate determination process, and has high sensitivity. The color change can be observed by the naked eye to judge whether there is thiosulfate in the solution. This method is simple to perform and is an improved method for the determination of thiosulfate in a desulfurization solution.

Downstream hydrochemistry and irrigation water quality of the Syr Darya, Aral Sea Basin, South Kazakhstan

Abstract New hydrochemical measurements from the Syr Darya provide insights into factors affecting the composition and quality of a major freshwater source replenishing the Aral Sea. This river is heavily used for power and irrigation and crosses territories of four Central Asia republics. It is intensely managed, draining several major tributaries, many reservoirs, and numerous irrigation distribution systems and canals. Analysis of seasonal changes in dissolved ion concentrations using geochemical diagrams, elemental ratios, statistical correlation, and equilibrium modeling allowed the characterization of mineral formation processes that control the dissolved chemical composition. Measured water hydrochemistry and composition type differs substantially from previous reports from the upper reaches of the Syr Darya in Kyrgyzstan. Element ratios, statistical correlation, and the presence of NO3- and NO2- suggest that the downstream trend of increasing total dissolved solids (TDS) from Zhetysay city to the Aral Sea in June is controlled by evaporation–crystallization processes, which contribute to the river dissolved load through soil runoff and return irrigation waters following leaching of secondary salts. Downstream sample composition during the growing season shows significant changes in magnesium-to-calcium ratios in the river water. Elevated magnesium levels in Syr Darya waters may pose a problem to sustainable uses for irrigation.

Soil evolution in basaltic parent materials under successive climate changes, Saudi Arabia

This study was designed to investigate the successive effects of the early Pleistocene subhumid and early to middle Holocene semi-arid paleoclimates and late Holocene to present day arid/hyperarid conditions on pedogenesis and evolution in Harrat Ithnayn volcano in the Arabian Shield, Saudi Arabia. The investigations were conducted using pedological macro and micro-features, physicochemical characteristics, elemental geochemistry, weathering indices and mineralogical analyses for light and heavy sand and clay fractions. The targeted soils developed in a subhumid paleoclimate and are classified as vitric Andisols, which are little to moderately weathered. Subhumid climate effects were evident through the presence of pedogenic Fe (crystalline oxides, Fed = 25 to 58 g kg─1), fairly high Feo/Fed (0.24 to 0.87), and the predominance of hydroxy-Al smectite and kaolinite. Residual primary minerals and modern arid conditions simultaneously led to accumulation of secondary salts and carbonates. Exchangeable Ca and Mg pools contributed 21–56 % of total Ca and Mg contents, while exchangeable K contributed only up to 4 %. Soil processes thus involved andisolization, salinization, and calcification. These processes were due to successive moist paleoclimates and the current arid conditions, thus revealing their formation under multiple climates.

HYDRO-GEOCHEMICAL EVALUATION AND APPLICATION OF WATER QUALITY INDEX (WQI) OF GROUNDWATER ON EAST COAST STRETCH OF TAMIL NADU, INDIA

The geochemical characteristics of 33 groundwater samples collected in and around the Kalpakkam area in 2019 were investigated, as well as the effects of seawater intrusion. The dominance of anions and cations is Cl- > HCO3- > NO3- > SO4 and Na+ > Mg >Ca> K. Electrical conductance has exceeded the allowable limit in the northeastern part of the study area, which could be accredited to the proximity of a backwater. The Cl (strong acid) predominates over HCO3 and SO4 (weak acids) in the groundwater of the study region during both seasons of 2019, 90.9 percent and 100%, respectively, based on the hydro-chemical features. The Water Quality Index was determined, and many of the 33 samples fell into the bad category, followed by the nice. The majority of anions and cations show a positive correlation (correlation matrix) with Cl-, especially Na and Mg, suggesting these ions may have been derived from seawater intrusion, secondary salt leaching, and chemical weathering, indicating both natural and anthropogenic origins. The interaction of the ions representing Mg, Ca, Na, and Cl in factors suggests secondary salt leaching or backwater recharge. The study's theme is to examine groundwater's geochemical signatures through geochemical analysis. Using statistical approaches, assess the impact of various pollution sources. The water quality index (WQI) is used to classify the quality of groundwater.

Preventing the secondary salt deterioration in the repaired area of basal erosion of earthen sites based on capillary barrier effect

Basal erosion is one of the most typical salt deteriorations of earthen sites in arid and semi-arid areas. Its formation is mainly related to the water and salt migration and enrichment at the bottom of earthen sites walls, and can cause collapse of site walls. Rammed roof-propping reinforcement is the main repair technology for the basal erosion of the earthen sites, but there is a risk of secondary salt deterioration in the repaired area due to the subsequent water and salt migration. Based on the capillary barrier theory, this study regulates the particle size composition of repair soil to explore repair materials that can effectively mitigate the secondary salt deterioration. Firstly, Arya-Paris model and Fredlund-Xing’s model were used to convert the particle size distribution curves (PSDC) of soil with different particle composition into soil–water characteristic curves (SWCC), to preliminarily judge the capillary barrier potential of different soil structures. Then carry out water-salt migration test and mercury intrusion porosimetry test to verify the predictions. The research shows that when repair soil is coarser than earthen site soil, it can form an effective capillary barrier to block the capillary rise of water and salt, thus reducing the secondary salt deterioration in the repaired area. When repair soil is finer than earthen site soil, it will promote the capillary rise of water and salt, thus aggravating the salt deterioration in the repaired area. It is proposed to use the repair material of adding 20% sand on the basis of the original earthen site soil particle composition for the rammed roof-propping reinforcement of the earthen sites.

Evaluating the influence of constant source profile presumption on PMF analysis of PM2.5 by comparing long- and short-term hourly observation-based modeling

Hourly PM2.5 speciation data have been widely used as an input of positive matrix factorization (PMF) model to apportion PM2.5 components to specific source-related factors. However, the influence of constant source profile presumption during the observation period is less investigated. In the current work, hourly concentrations of PM2.5 water-soluble inorganic ions, bulk organic and elemental carbon, and elements were obtained at an urban site in Nanjing, China from 2017 to 2020. PMF analysis based on observation data during specific pollution (firework combustion, sandstorm, and winter haze) and emission-reduction (COVID-19 pandemic) periods was compared with that using the whole 4-year data set (PMFwhole). Due to the lack of data variability, event-based PMF solutions did not separate secondary sulfate and nitrate. But they showed better performance in simulating average concentrations and temporal variations of input species, particularly for primary source markers, than the PMFwhole solution. After removing event data, PMF modeling was conducted for individual months (PMFmonth) and the 4-year period (PMF4-year), respectively. PMFmonth solutions reflected varied source profiles and contributions and reproduced monthly variations of input species better than the PMF4-year solution, but failed to capture seasonal patterns of secondary salts. Additionally, four winter pollution days were selected for hour-by-hour PMF simulations, and three sample sizes (500, 1000, and 2000) were tested using a moving window method. The results showed that using short-term observation data performed better in reflecting immediate changes in primary sources, which will benefit future air quality control when primary PM emissions begin to increase.

Cyclic degradation of thiocyanate in cyanide barren solution by manganese oxides

This study describes the degradation of thiocyanate by manganese oxides. With NaOH and CaO as precipitating agents, two manganese oxides, i.e. MnOx/Na and MnOx/Ca, were prepared using MnSO4·H2O as Mn resource and air as oxidant. The influence of various reaction parameters like pH, manganese oxide dosage and initial thiocyanate concentration were systematically investigated with MnO2 as a reference. Based on an entire process dynamics model and the initial kinetics analysis, the rate-limiting step (formation of the precursor complexes) and reaction orders were derived independently. The reaction pathway was detected and the formation of the precursor complexes between surface positively charged manganese oxides and thiocyanate was the first step of thiocyanate degradation, after which electron transfer occurred within the precursor complexes and intermediate products were formed, which were rapidly released to produce SO42− and CN−, and some of the CN− would be further oxidized to HCO3− and NH4+. The formation of precursor complexes is related to the charge distribution on the surface of the manganese oxide and the protonation of thiocyanate in solution, which makes the lower pH favorable. The results of cyclic treatment of cyanide barren solution showed good regenerability of MnOx/Ca and gradual reduction of undesired secondary salts (especially SO42− ions) in the degraded liquid, which made it a potentially reliable technique to regulate the thiocyanate concentration during the cyanidation process of gold ores economically.

Preventing the Secondary Salt Deterioration in the Repaired Area of Basal Erosion of Earthen Sites Based on Capillary Barrier Effect

Preventing the Secondary Salt Deterioration in the Repaired Area of Basal Erosion of Earthen Sites Based on Capillary Barrier Effect

Impact of secondary salts, temperature, and pH on the colloidal stability of graphene oxide in water.

The stability of graphene oxide (GO) in water is extremely relevant because of its application as an adsorbent material, as well as for its fate and behavior in the environment. Zeta potential was used to study the effect of secondary salts (carbonate, sulfate, and phosphate), temperature (20 to 60 °C), and pH (5 to 9) on the stability of six different GOs produced from natural, synthetic, and amorphous graphite—with and without the use of attrition milling. Generally, GOs produced with attrition-milled graphites had lower ζ-potentials than their unmilled counterparts because of their smaller particle sizes and higher concentration of oxygen-containing functional groups. It was observed that GO produced from graphite and synthetic graphite had ζ-potential values lower than −30 mV, even at 30 °C. However, it was observed that all the GOs studied were unstable in the presence of carbonate and sulfate salts at concentrations between 170 and 1695 mg L−1, as they reached a ζ-potential of −4.1 mV. Density-functional theory electronic structure calculations suggested that the instability of GO in the presence of carbonate and sulfate was caused by the abstraction of a proton resulting in interaction energies Eint of 28.3 and 168.9 kJ mol−1, respectively. Our results suggest that temperatures above 30 °C, as well as carbonate and sulfate salts at concentrations relevant to arid and semi-arid regions, could promote the formation of agglomerates of GO, thus limiting its use and mobility in water.

Appraisal of the Quality Parameters of the Groundwater used for Domestic and Irrigation Purposes in the Hard Rock Aquifer System of the Vasishta sub- basin of the Vellar River, Tamil Nadu


 
 
 
 This article presents an appraisal of the quality of groundwater in the hard Received in revised form: 15.07.2021 rock aquifer system of the Vasishta sub basin, of the Vellar River Basin. Seventy nine representative groundwater samples were collected from dug and bore wells which are intensively used for domestic and irrigational purposes. The physical parameters viz. PH, EC and TDS were estimated in the field using a portable multiparameter meter. The groundwater samples were transported to the laboratory for measuring major ionic concentrations viz, Ca, Mg, Na, K, CO3, HCO3, Cl, SO4, F and NO3. The hydrochemical data were graphically projected and spatial temporal thematic maps generated with reference to the World Health Organization (WHO) and Bureau of Indian (BIS) Standards. The peoples living in the sub basin engage in agricultural activities where the groundwater availability is sufficient. The groundwater is a major source for meeting their basic needs, such as for domestic, irrigational and industrial purposes. Good correlation is exhibited between EC and TDS Cl, SO4.Cl exhibits good correlation with Mg and Ca (0.817), (0.751) indicating leaching of secondary salts. TDS and EC showed strong correlation with Cl, SO4. Clustering groundwater samples based on their similarity is known as Q-mode type clustering method. Spatial and temporal maps of the water quality index reveal that the majority of the groundwater samples fall under the categories excellent to good.
 
 
 

Groundwater quality assessment for irrigation use in the Godavari Delta region of east coast India using IRWQI and GIS

Abstract The present work was carried out in the deltaic region of the river Godavari in coastal Andhra Pradesh of southern India to evaluate the status of groundwater quality for irrigation. Groundwater is predominantly used in these productive agricultural fields. Saline water intrusion in fresh groundwater aquifers, which is mainly due to the excess withdrawal of groundwater, was recorded in the study area. A total of 80 groundwater samples were analyzed for physical and chemical parameters using standard chemical procedures. The groundwater mainly represents Na+–Cl− type, which shows the mixing of fresh water with saline water. The high correlation between Na+–Cl− and Mg2+–HCO3− explained that the intermixing of aquifer waters and the leaching of secondary salts influenced the region. Evaporation-fractional crystallizations are the main processes in the groundwater of the study area. The irrigation water quality index was calculated using different quality indices including Na%, sodium adsorption ratio, residual sodium bicarbonate (RSBC), permeability index (PI), magnesium hazard (MH), Kelly's ratio (KR), and potential salinity (PS), Cl−:HCO3−, Mg2+:Ca2+ and Na+:Ca2+ to estimate the suitability of groundwater quality for irrigation. Spatial distribution maps were prepared using raster interpolation in GIS. The assessment revealed that the areas covering 67.6% of electrical conductivity, 100% of total dissolved solids, 57.5% of Na%, 21.3% of RSBC, 66.3% of PI, 16.3% of MH, 65% of KR, and, 100% of PS required severe to moderate restrictions. Overall, the groundwater in the study region showed potential salinity due to geogenic and anthropogenic activities, and thus it must be monitored for sustainable agriculture.

The Role of Calcite Dissolution and Halite Thermal Expansion as Secondary Salt Weathering Mechanisms of Calcite-Bearing Rocks in Marine Environments

This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of salt-saturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments.

Differences in evaporite geochemistry of the greater Ordos Ordovician salt basin, China: evidence from the M56 submember of the Majiagou Formation

Ordovician evaporites are very rare in the global geological record. Thick salt deposits in the Ordovician Majiagou Formation are present in the eastern greater Ordos Basin, China. Potash mineralization layers and a thin industrial grade potash layer occur in the sixth submember of the fifth member of the formation, thus indicating a good potash prospect. The eastern and western salt depressions are separated by an uplift and have been divided into five secondary salt sags (East-1, East-2, West-1, West-2, and West-3). The ratio of the salt layer thickness to that of the whole succession was very low in the West-2 sag and the salt depositional center was the East-2 sag, which implied that seawater entered the basin from the western sags and led to desalination and the formation of deep-water sediments. Analyses indicated that the potash formation conditions were obviously different in the salt sags. Although a thin potash layer was present in the East-1 sag, findings indicated that this area was not favorable for potash accumulation. The geochemical and sedimentary environment of the East-2 sag was similar to that of typical potash basins globally. Rounded sylvine grains occurred between salt crystals. The preservation characteristics indicated that evaporite deposits had reached the KCl bitterns stage. An eastward input of terrestrial materials carried a large amount of clay, and the clay layer protected previously deposited sylvine particles, thereby avoiding further potassium dissolution. Sedimentary, geochemical, and petrological evidences indicate good prospects for potash exploration in the East-2 salt sag.

The role of carboxyl groups upon the precipitation of albumin at low pH

Proteins play a major role in the organization of the living matter. Underlying this fact are their unique properties in aqueous solution, for which the available theories provide only a partial explanation. In order to throw some light into the behaviour of proteins in aqueous solution, experiments on the precipitation of electropositive albumin by means of the sodium salts of sulfate, thiocyanate, nitrate, bromide and chloride upon varying the solution pH were undertaken. Results show that the protein undergoes a transition at approximately pH 3, characterized by a change on its precipitation profile. Its shape, of monotonic profile below pH 3, displays a non-monotonic behaviour with separated peaks at higher pH values, which increase in number and decrease in intensity with increasing pH. To elucidate these observations, additional precipitation experiments with sodium thiocyanate in the presence of a secondary salt were undertaken. It is shown that the secondary salt changes significantly the protein's precipitation profile, despite being present in very low concentration. Its influence on the precipitation depends in a great extent on the cation's valence, which induce effects proportional to x, x2, and x3 for monovalent, divalent, and trivalent cations, respectively. The observations reported can be explained under the assumption that i) the protein dissociates into distinct forms, as result of the dissociation of carboxyl groups, and ii) salt cations establish chemical equilibria with the negative charges of the dissociated carboxyl groups present in the emerging protein forms.