Reactions Of Silicate Minerals Research Articles

Nanoscale control over water-film thickness using temperature modulation: tuning mineral carbonation reactivity

Temperature modulation was demonstrated as a novel way to control water partitioning during the reaction of silicate minerals with water-saturated supercritical carbon dioxide.

Geochemical Characterization of Surface Waters and Groundwater Resources in the Gharye-Alarab Basin, Southeastern Iran

This paper reports new geochemical data on dissolved major and minor constituents in surface waters and groundwater collected in the Gharye-Alarab basin (south-eastern Iran) and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area. A total of 31 water samples were collected in this study area, including 11 rivers and 20 groundwater samples, and analyzed for temperature, pH, Eh, electrical conductivity, total dissolved solids, major ions and 18 trace elements concentrations. The most waters were grouped into Ca–Mg–HCO3 type. Reaction of silicate minerals is a key responsible for geochemical processes in the study area. Trace elements concentrations are low and Surface waters have lower trace element abundances compared to groundwater. Arsenic compared with other trace elements; shows a rather wide concentration range in the sampled waters, ranging between 0.6 to 502 µg/l and is not correlated with pH and Eh in surface water but are a function of pH and Eh in groundwater.

Aqueous alteration of chondrules from the Murchison CM carbonaceous chondrite: Replacement, pore filling, and the genesis of polyhedral serpentine

AbstractForsterite and clinoenstatite in type IAB chondrules from the Murchison CM carbonaceous chondrite have been partially serpentinized, and the mechanisms of their alteration reveal crystallographic and microstructural controls on the reaction of silicate minerals with parent body aqueous solutions. Grains of forsterite were altered in two stages. Narrow veinlets of Fe‐rich serpentine formed first and by the filling of sheet pores. Most of these pores were oriented parallel to (010) and (001) and had been produced by earlier fracturing and/or congruent dissolution. In the second stage, the subset of veinlets that were oriented parallel to (001) was widened accompanying the replacement of forsterite by Mg‐Fe serpentine. This reaction proceeded most rapidly parallel to [001], and crystallographic controls on the trajectory of retreating vein walls created fine‐scale serrations. Murchison clinoenstatite grains have a skeletal appearance due to the presence of abundant veinlets and patches of phyllosilicate. Two alteration stages can again be recognized, with initial water–mineral interaction producing tochilinite‐rich veinlets by the filling of (001)‐parallel contraction cracks. Pores then formed by congruent dissolution that was guided principally by orthopyroxene lamellae, and they were subsequently filled by submicrometer‐sized crystals of polyhedral serpentine. This finding that Murchison forsterite and clinoenstatite grains have been altered demonstrates that aqueous processing of magnesium silicate minerals started much earlier in CM parent body history than previously believed. Our results also show that the occurrence of polyhedral serpentine can be used to locate former pore spaces within the parent body.

English

Growing populations and increasing industrialization causes increase in living standard, which result in decrease in the quality of water and may put stresses on natural waters by impairing both the quality of the water and the hydrological budget. This research aimed at determining the origin of the chemical elements of groundwater from the Oran Sebkha basin. It applied the inverse geochemical modeling to derive the sources of variation in the hydrochemistry. Fifty five (55) water samples were selected from different point in Oran Sebkha basin for sampling purpose in July 2011. Physico-chemical parameters such as pH and electric conductivity were measured in situ . Moreover, chloride, sulfate, alkalinity, calcium, magnesium, sodium, potassium, were measured in the laboratory. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the chemical reactions controlling water chemistry. The inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into three categories: (1) dissolution of evaporite minerals; (2) precipitation of carbonate minerals; and (3) weathering reactions of silicate minerals. The high values of the physico-chemical parameters of water obtained in the present study sites indicate a variation in the physico-chemical parameters and demonstrated that relatively few phases are required to derive water chemistry in the area. Range of values were found as pH (5.1-7.6), conductivity (720-15820 μS cm -1 ), chloride (994-7810 mg l -1 ), sulfate (6.1-112.4 mg l -1 ), alkalinity (421-19962 mg l -1 ), calcium (80-680 mg l -1 ), magnesium (212.4-4525 mg l -1 ), sodium (124.2-4687.4 mg l -1 ) and potassium (0.9-42.5 mg l -1 ). Key words : Physico-chemical parameters, water, Sebkha.

87Sr/86Sr, δ18O およびδ13C が示す石灰質砂岩炭酸塩の生成過程

87Sr/86Sr, δ18O およびδ13C が示す石灰質砂岩炭酸塩の生成過程

Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater

A 6,500-year diatom stratigraphy has been used to infer hydrochemical changes in Lake Awassa, a topographically closed oligosaline lake in the Ethiopian Rift Valley. Conductivity was high from ~6400-6200 BP, and from 5200-4000 BP, with two brief episodes of lower conductivity during the latter period. Although the timing of the conductivity changes is similar to the timing of lake-level change in the nearby Zwai-Shalla basin, their directions are the reverse of that expected from a climatic cause. Dissolution of the tephras which precede both phases of high conductivity cannot explain the increases in salinity, because rhyolitic tephras are only sparingly soluble. Instead, the pulsed input of groundwater made saline by the reaction of silicate minerals and volcanic glass with carbonic acid, formed from the solution of carbon dioxide degassed from magma under the Awassa Caldera, is suggested as a plausible mechanism for the observed change in lake chemistry. Diatom-inferred hydrochemistry cannot therefore be used to reconstruct climate change in Lake Awassa.

Hydrochemical evolution of the East Midlands Triassic sandstone aquifer, England

A detailed hydrogeochemical interpretation has been made of the red-bed, Sherwood Sandstone (Triassic) aquifer of the East Midlands of England, on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line. Groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions; cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water. Three distinct zones are recognised: 1. I. Recent groundwater (mainly < 100 y), oxidising, dominated by congruent dissolution of dolomite, and by inputs from atmospheric and anthropogenic sources. 2. II. Groundwater age 10 3–10 4 y, predominantly reducing, dominated by incongruent dissolution of dolomite. 3. III. Groundwater age > 10 4 y, reducing conditions, approach to isotopic and chemical equilibrium in the carbonate system, dominance of gypsum dissolution. The minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history. Na +, Cl −, F − and B are controlled by atmospheric inputs. Sr 2+ and Mn 2+ trends can be explained by carbonate and sulphate mineral dissolution; Ba 2+ is derived from carbonates but controlled by barite equilibrium. Fe, SO 4 2−, NO 3 − and U are strongly influenced by redox reactions. The concentrations of transition metals and other elements remain very low. Only Li + and K + are considered to represent additions by reaction of silicate minerals. The extent of direct anthropogenic influence is probably limited to enhanced SO 4 −, NO 3 2− and possibly Cu, Zn and Pb in Zone I.