In-situ-Investigations of Physico-Chemical Processes at Interfaces

AbstractAt the Ashanti concession, Ghana, gold-bearing quartz veins and disseminated sulphide lodes occur in narrow (1-3 m) shear zones with altered argillites and metatholeiite host rocks. The mineralisation is concealed by up to 10 m of kaolinite-mica forest ochrosol soils, beneath which is a saprolitic zone of leached rock extending down 60-70 m to the hypogene ore zone. In the unweathered hypogene orebody, gold occurs as free grains in quartz, as sub-microscopic inclusions in the disseminated arsenopyrite, as gold tellurides and as aurostibite. The gold is released from the hypogene orebody by physical dissaggregation and chemical dissolution, the latter involving hydroxyl, thiosulphate, cyanide, and fulvate complexing. Dissolution and reprecipitation of the gold appears to have taken place largely in situ with little evidence of supergene enrichment. Consequently, the gold mineralogy of the soils is complex with residual and secondary gold grains exhibiting widely different textural and compositional characteristics. Residually enriched grains display pitted, rounded surfaces and have silver-depleted rims, while supergene gold grains are compositionally homogenous and have unpitted surfaces. The supergene grains display platelet, dendritic, irregular and octahedral habit. A fine grained spongy form of gold has also been observed from weathered telluride-bearing quartz veins. Much of the secondary gold is intergrown with iron oxides and hydroxides. The gold mineralogy of the Ashanti soils appears to be controlled by physico-chemical processes active during the lateritic pedogenesis producing residual and supergene enrichment of gold.

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On the development of internal chemical zonation in small mafic dykes

Geological Magazine ◽

10.1017/s0016756809990343 ◽

2009 ◽

Vol 147 (1) ◽

pp. 1-12 ◽

Cited By ~ 23

Author(s):

SOFYA CHISTYAKOVA ◽

RAIS LATYPOV

Keyword(s):

Chemical Processes ◽

Complete Understanding ◽

Abrupt Increase ◽

Mafic Dykes ◽

Physico Chemical ◽

Geochemical Study ◽

Flow Differentiation ◽

Compositional Pattern

AbstractThree dolerite dykes (Small, 3.2 cm; Middle, 13.5 cm; Thick, 50 cm) from Torsholma Island, SW Finland, reveal distinctly different internal zonation that becomes more complicated with increasing thickness of the dykes. The Small Dyke shows a systematic inward increase in normative Pl (An+Ab+Or) and a decrease in normative An (100*An/(An+Ab)), whole-rock MgO, Mg number (100*Mg/(Mg+Fetotal)), TiO2, K2O and Zr. The Middle Dyke exhibits the same compositional pattern at the margins, while the centre is distinguished by an abrupt increase in normative Pl and An, whole-rock Sr and Mg number. From the margins inwards, the Thick Dyke displays first a compositional pattern identical to that observed in the Small Dyke and the margins of the Middle Dyke. This is followed by a region where whole-rock MgO, Mg number and normative An start increasing inwards, while the transition to the centre of the dyke is characterized by a compositional pattern similar to that in the centre of Middle Dyke. The origin of chemical zonation in these dykes is attributed to the operation of three independent physico-chemical processes, namely: the Small Dyke formed exclusively by progressive changes in the composition of inflowing magma; the Middle Dyke by changes in composition of inflowing magma (margins) and concentration of plagioclase and olivine phenocrysts by flow differentiation (centre); the Thick Dyke by changes in composition of inflowing magma (margins),in situcumulate growth against dyke sidewalls (middle) and flow differentiation (centre). Systematic changes in these processes and, as a result, in internal chemical zonation, likely take place in response to crystallization of magma under less supercooled conditions with increasing dyke thickness. A comprehensive geochemical study of the internal zonation of small mafic dykes worldwide is required to develop a complete understanding of the processes operating in mafic dykes.

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Nucleophilicity and its parametrization

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19890117 ◽

1989 ◽

Vol 54 (1) ◽

pp. 117-135

Author(s):

Oldřich Pytela ◽

Vítězslav Zima

Keyword(s):

Regression Analysis ◽

Linear Correlation ◽

Correlation Equation ◽

Chemical Processes ◽

General Tendency ◽

Orbital Interaction ◽

Physico Chemical ◽

Physical And Chemical ◽

Two Parameter ◽

Better Than

The method of conjugate deviations based on the regression analysis has been suggested for construction of a new nucleophilicity scale. This method has been applied to a set of 28 nucleophiles participating in 47 physical and chemical processes described in literature. The two-parameter nucleophilicity scale obtained represents-in the parameter denoted as ND-the general tendency to form a bond to an electrophile predominantly on the basis of the orbital interaction and-in the parameter denoted as PD-the ability to interact with a centre similar to the proton (basicity). The linear correlation equation involving the ND, PD parameters and the charge appears to be distinctly better than the most significant relations used. The correlation dependences have the physico-chemical meaning. From the position of individual nucleophiles in the space of the ND and PD parameters, some general conclusions have been derived about the factors governing the reactivity of nucleophiles.

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In situ dual crosslinking strategy to improve the physico-chemical properties of thermoplastic starch

Carbohydrate Polymers ◽

10.1016/j.carbpol.2021.118250 ◽

2021 ◽

pp. 118250

Author(s):

Hamed Peidayesh ◽

Abolfazl Heydari ◽

Katarína Mosnáčková ◽

Ivan Chodák

Keyword(s):

Chemical Properties ◽

Thermoplastic Starch ◽

Physico Chemical

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Enzymes at solid surfaces: Nature of the interfaces and physico-chemical processes

Electrochimica Acta ◽

10.1016/j.electacta.2008.02.100 ◽

2008 ◽

Vol 54 (1) ◽

pp. 116-122 ◽

Cited By ~ 23

Author(s):

Samuel Caillou ◽

Patrick A. Gerin ◽

Cristèle J. Nonckreman ◽

Sandrine Fleith ◽

Christine C. Dupont-Gillain ◽

...

Keyword(s):

Chemical Processes ◽

Solid Surfaces ◽

Physico Chemical

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Removal of heavy metal from soil and groundwater by in-situ electrokinetic remediation

Water Science & Technology ◽

10.2166/wst.2000.0586 ◽

2000 ◽

Vol 42 (7-8) ◽

pp. 335-343 ◽

Cited By ~ 4

Author(s):

S. Shiba ◽

S. Hino ◽

Y. Hirata ◽

T. Seno

Keyword(s):

Heavy Metals ◽

Heavy Metal ◽

Electric Potential ◽

Potential Gradient ◽

Electrokinetic Remediation ◽

Contaminated Aquifer ◽

Physico Chemical ◽

Operational Variables ◽

Mass Transport Process

The operational variables of electrokinetic remediation have not been cleared yet, because this method is relatively new and is an innovative technique in the aquifer remediation. In order to investigate the operational variables of the electrokinetic remediation, a mathematical model has been constructed based on the physico chemical mass transport process of heavy metals in pore water of contaminated aquifer. The transport of the heavy metals is driven not only by the hydraulic flow due to the injection of the purge water but also by the electromigration due to the application of the electric potential gradient. The electric potential between anode and cathode is the important operational variable for the electrokinetic remediation. From the numerical simulations with use of this model it is confirmed that the remediation starts from the up stream anode and gradually the heavy metal is transported to the down stream cathode and drawn out through the purge water.

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Some indicators of water quality of the Tamis river

Chemical Industry and Chemical Engineering Quarterly ◽

10.2298/ciceq100712060b ◽

2011 ◽

Vol 17 (1) ◽

pp. 107-115 ◽

Cited By ~ 3

Author(s):

Nada Babovic ◽

Dejan Markovic ◽

Vojkan Dimitrijevic ◽

Dragan Markovic

Keyword(s):

Water Quality ◽

Ph Value ◽

Ammonium Nitrogen ◽

Field Analysis ◽

Total Hardness ◽

Chemical Parameters ◽

Physico Chemical

This paper shows the results obtained in field analysis performed at the Tamis River, starting from the settlement Jasa Tomic - border between Serbia and Romania to Pancevo - confluence of Tamis into the Danube. The Tamis is a 359 km long river rising in the southern Carpathian Mountains. It flows through the Banat region and flows into the Danube near Pancevo. During the years the water quality of the river has severely deteriorated and badly affected the environment and the river ecosystem. In situ measurements enabled determination of physico-chemical parameters of water quality of the Tamis River on every 400 m of the watercourse, such as: water temperature, pH value, electrical conductivity, contents of dissolved oxygen and oxygen saturation. The main reason of higher pollution of Tamis is seen in connection to DTD hydro system. Sampling was performed at 7 points with regard to color, turbidity, total hardness, alkalinity, concentration of ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, iron, chlorides and sulphates in samples. The aim of the present work was to evaluate water quality in the Tamis River taking into account significant pollution, which originates from settlements, industry and agriculture, and to suggest appropriate preventive measures to further pollution decreasing of the river's water.

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