Geochemical modeling of chromium release in natural waters and treatment by RO/NF membrane processes

Arsenic (As) is a toxic element present in different natural systems. The aqueous As species and their concentrations in natural waters depend on a variety of parameters, including the presence of natural source and the local geochemical conditions. The primary source of As in natural waters is the oxidation of mineral sulphides like arsenopyrite (FeAsS) and As-rich pyrite (FeS2) [1]. The trivalent iron (Fe3+) can act as oxidant for pyrite oxidative dissolution together with dissolved oxygen.In this work the attention is focused in As- contaminated area of the Calabria Region (Southern Italy). The high arsenic concentration is a peculiar characteristic of the shallow groundwaters circulating in a limited area of the Calabria region, which represents an unexplored mineralized area. Indeed, although pyrite is widely present in the crystalline rocks, its spatial distribution is highly variable and not predicable [2]. Generally, the As content of the studied granite rocks is within the normal global range but the presence of not-surfacing, hydrothermally-altered granites, could be the cause of As contamination in limited areas. &#160;In order to explain the As-rich groundwaters occurring into crystalline aquifer, a reaction path modelling of granite dissolution was performed by using EQ3/6 software package version 8a.&#160; The dissolving granite was considered to be constituted by quartz, two types of plagioclase (representing the rim and the core of the mineral), K-feldspar, biotite, muscovite, chlorite, epidote, fluorapatite and pyrite. &#160;The considered value of pyrite content and its As concentration fall within the global estimations [3]. Two simulations were performed allowing the precipitation of moganite, gibbsite, kaolinite, illite-py and the calcite-rich solid solution of trigonal carbonate. Moreover, two oxy-hydroxide solid solutions composed of amorphous Fe(OH)3 - amorphous ferric arsenate and 2 lines-ferrihydrite - scorodite were precipitated in two separate runs to evaluate their effects on dissolved As. Nine water samples were used to fix the boundary conditions as well as to validate the outcomes of geochemical modeling. The arsenic concentration detected ranging from 25 to 435 &#181;g/L. The theoretical trend involving the precipitation of amorphous Fe(OH)3 is in agreement with the groundwaters richest in As, because a higher amount of pyrite is dissolved due to a greater availability of trivalent Fe in the aqueous solution, which is caused by the higher solubility of amorphous Fe(OH)3 compared to 2-line ferrihydrite. The analytical data of the As-rich groundwaters, as a whole, are well explained by the performed simulations, suggesting that these processes control the release and fate of arsenic during the water-rock interaction.&#160;[1]. Sracek, O., Bhattacharya, P., Jacks, G., Gustafsson, J. P., & Von Br&#246;mssen, M. ,2004. Behavior of arsenic and geochemical modeling of arsenic enrichment in aqueous environments. Applied Geochemistry, 19(2), 169-180.[2]. Bonardi G., De Vivo B., Giunta G., Lima A., Perrone V., Zuppetta A., 1982. Mineralizzazioni dell&#8217;Arco Calabro Peloritano.Ipotesi genetiche e quadro evolutivo. Boll.Soc.Geol.It. 101[3]. Smedley, P. L., & Kinniburgh, D. G.,2002. A review of the source, behaviour and distribution of arsenic in natural waters.&#160;Applied geochemistry,&#160;17(5), 517-568.

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Calorimetric determination of the enthalpies of formation of hydrotalcite-like solids and their use in the geochemical modeling of metals in natural waters

Clays and Clay Minerals ◽

10.1346/ccmn.2006.0540401 ◽

2006 ◽

Vol 54 (4) ◽

pp. 409-417 ◽

Cited By ~ 26

Author(s):

Rama Kumar Allada ◽

Edward Peltier ◽

Alexandra Navrotsky ◽

William H. Casey ◽

C. Annette Johnson ◽

...

Keyword(s):

Natural Waters ◽

Geochemical Modeling ◽

Enthalpies Of Formation ◽

Calorimetric Determination

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Introduction

Geochemical Reaction Modeling ◽

10.1093/oso/9780195094756.003.0005 ◽

1996 ◽

Author(s):

Craig M. Bethke

Keyword(s):

Natural Waters ◽

Geochemical Modeling ◽

Computer Programs ◽

Solution Chemistry ◽

Rate Equations ◽

Injection Wells ◽

Irreversible Reaction ◽

Quantitative Models ◽

Geothermal Wells ◽

Hand Calculation

As geochemists, we frequently need to describe the chemical states of natural waters, including how dissolved mass is distributed among aqueous species, and to understand how such waters will react with minerals, gases, and fluids of the Earth's crust and hydrosphere. We can readily undertake such tasks when they involve simple chemical systems, in which the relatively few reactions likely to occur can be anticipated through experience and evaluated by hand calculation. As we encounter more complex problems, we must rely increasingly on quantitative models of solution chemistry and irreversible reaction to find solutions. The field of geochemical modeling has grown rapidly since the early 1960s, when the first attempt was made to predict by hand calculation the concentrations of dissolved species in seawater. Today's challenges might be addressed by using computer programs to trace many thousands of reactions in order, for example, to predict the solubility and mobility of forty or more elements in buried radioactive waste. Geochemists now use quantitative models to understand sediment diagenesis and hydrothermal alteration, explore for ore deposits, determine which contaminants will migrate from mine tailings and toxic waste sites, predict scaling in geothermal wells and the outcome of steam-flooding oil reservoirs, solve kinetic rate equations, manage injection wells, evaluate laboratory experiments, and study acid rain, among many examples. Teachers let their students use these models to learn about geochemistry by experiment and experience. Many hundreds of scholarly articles have been written on the modeling of geochemical systems, giving mathematical, geochemical, mineralogical, and practical perspectives on modeling techniques. Dozens of computer programs, each with its own special abilities and prejudices, have been developed (and laboriously debugged) to analyze various classes of geochemical problems. In this book, I attempt to treat geochemical modeling as an integrated subject, progressing from the theoretical foundations and computational concerns to the ways in which models can be applied in practice. In doing so, I hope to convey, by principle and by example, the nature of modeling and the results and uncertainties that can be expected. Hollywood may never make a movie about geochemical modeling, but the field has its roots in top-secret efforts to formulate rocket fuels in the 1940s and 1950s.

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