Spatial evolution of an AMD stream in the Iberian Pyrite Belt: process characterization and control factors on the hydrochemistry

This paper presents hydrochemical data of an AMD stream in the Iberian Pyrite Belt, obtained from its source, in the Poderosa Mine Portal, till its confluence at the Odiel River. The main objective is to establish potential interdependent relations between sulfate and metals’ loads and the following physical-chemical variables: pH, electric conductivity (EC), redox potential (EH), and dissolved oxygen (O2). All the parameters show a global increasing tendency since the tunnel’s exit to the confluence at Odiel River. The TDS and EC are two relevant exceptions. They behave similarly, showing a decreasing trend and a strong inflection that describes a minimum immediately after the discharging point. The spatial analysis combined with statistical tools put in evidence the typical AMD processes and the respective physical-chemical implications. Inputs with distinctive hydrochemical signatures impose relevant modifications in the Poderosa creek waters. This indicates low hydrochemical inertia and high vulnerability to external stimulus.Financial support for this research was provided by DGCICYT National Plan, project CGL2010-21268-C02-01 and the Andalusian Autonomous Government Excellence Projects, Project RNM-6570

Moral spaces, and sexual transgression: understanding rape in war and post conflict

When it comes to rape in war, evocative language describing rape as a ‘weapon of war’ has become commonplace. Although politically important, overemphasis on strategic aspects of wartime sexual violence can be misleading. Alternative explanations tend to understand rape either as exceptional — a departure from ‘normal’ sexual relationships — or as part of a continuum of gendered violence. This article shows how, even in war, norms are not suspended; nor do they simply continue. War changes the moral landscape. Drawing on ethnographic research over 10 years in northern Uganda, this article argues for a re-sexualization of understandings of rape. It posits that sexual mores are central to explaining sexual violence, and that sexual norms — and hence transgressions — vary depending on the moral spaces in which they occur. In Acholi, moral spaces have temporal dimensions (‘olden times’, the ‘time of fighting’ and ‘these days’) and associated spatial dimensions (home, camp, bush, village, town). The dynamics of each help to explain the occurrence of some forms of sexual violence and the rarity of others. By reflecting on sexual norms and transgressions in these moral spaces, the article sheds light on the relationship between ‘event’ and ‘ordinary’, rape and war

Thermodynamic properties for arsenic minerals and aqueous species

Quantitative geochemical calculations are not possible without thermodynamic databases and considerable advances in the quantity and quality of these databases have been made since the early days of Lewis and Randall (1923), Latimer (1952), and Rossini et al. (1952). Oelkers et al. (2009) wrote, “The creation of thermodynamic databases may be one of the greatest advances in the field of geochemistry of the last century.” Thermodynamic data have been used for basic research needs and for a countless variety of applications in hazardous waste management and policy making (Zhu and Anderson 2002; Nordstrom and Archer 2003; Bethke 2008; Oelkers and Schott 2009). The challenge today is to evaluate thermodynamic data for internal consistency, to reach a better consensus of the most reliable properties, to determine the degree of certainty needed for geochemical modeling, and to agree on priorities for further measurements and evaluations. Recent attention has been directed to arsenic (As) thermodynamic data, partly because of the worldwide recognition of arsenic poisoning in more than 70 countries (Nordstrom 2002; Ravenscroft et al. 2009) and the need to interpret As mobility more quantitatively in groundwater and surface-water systems. Unfortunately, not as many useful thermodynamic measurements have been made on reactions involving As compared to other major solutes and trace elements. Grenthe et al. (1992), when reviewing As data for the Organization for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA) thermodynamic database on U, stated “Although needed, a complete reanalysis of the chemical thermodynamic data for arsenic species is not within the scope of the current review.” Although a complete reanalysis is not feasible at this time, this chapter reviews As thermodynamic data with a focus on internal consistency and the quality of the original measurements, updates with new data, points out some areas of discrepancies, makes recommendations for the resolution of some properties, and suggests avenues for further investigations

Solubility and thermodynamic data for metal arsenates

Reliable and consistent thermodynamic data for arsenic minerals and aqueous species are required given the worldwide recognition of As poisoning in more than 70 countries [1] and the need to model As mobility more quantitatively in groundwater systems. Arsenic contamination can also constitute a serious problem in hydrometallurgical processing [2]. Unfortunately, few useful thermodynamic measurements have been made on reactions involving As minerals because of experimental difficulties, including long equilibration times with aqueous solutions, formation of metastable phases, and effects of crystallinity and particle-size on solubilities [3]. Solutions to these impediments are discussed in this review of solubility and thermodynamic data for Fe(III) [4] and Ca arsenates, and for solid solutions of arsenates with phosphates and vanadates [5]. We will present models for solubility calculations that utilize the most recent critical evaluation of the thermodynamic properties of arsenic species [6]. We will also make recommendations for the resolution of some discrepancies and suggest directions for further investigations

Critical evaluation of thermodynamic data for selected arsenic minerals and aqueous species with applications to natural waters

A critical evaluation of selected arsenic minerals and aqueous species and a separate review of aqueous arsenic speciation were completed recently as part of a new volume on arsenic geochemistry, mineralogy, toxicity, and microbiology (Reviews in Mineralogy and Geochemistry #79). We developed a thermodynamic network based on the most reliable and fundamental data in the arsenic system, using the most direct pathways to build the network, and checking for internal consistency at each step. Arsenolite, As2O3-cubic, is the cornerstone or anchor of the network from which thermodynamic properties of the aqueous species of arsenate and arsenite and their hydrolysis products are derived. Thermodynamic data on aqueous arsenate ions are essential for the evaluation of metal arsenate minerals and their solubilities. Very few measurements of metal arsenate and metal arsenite complexes are reported from the literature but by using a consistent chemical model and the same equation of state, several metal arsenate and metal arsenite complexes have been estimated by Marini and Accornero (2007, Environ. Geol. 52, 1343). The solubilities and solubility-product constants of several metal arsenates have been reported but many are of variable quality and in need of better measurements and further evaluation. Scorodite solubility is well characterized, consistent with recent calorimetric data at ambient temperatures. The solubility of some calcium arsenates is well characterized and there is some agreement between investigations but inconsistencies still exist and some phases are poorly characterized or not measured at all. Application of estimated metal-arsenate and metal-arsenite stability constants to waters with a wide range of composition and temperature shows that arsenite speciation is affected very little (98-99% as free forms of hydrolyzed arsenite) but that arsenate speciation can be affected substantially (24-71% of the arsenate species in the free forms). Calcium and magnesium arsenate complexes contribute 0-24%, and sodium arsenate complexes contribute 1.5-75%. These complexes should be included in speciation calculations for any waters involving arsenate species, especially water compositions with moderate or higher concentrations of sodium

Ground water chemistry and geochemical modeling of water-rock interactions at the Osamu Utsumi mine and the Morro do Ferro analogue study sites, Poços de Caldas, Minas Gerais, Brazil.

Surface and ground waters, collected over a period of three years from the Osamu Utsumi uranium mine and the Morro do Ferro thorium/rare-earth element (Th/REE) deposits, were analyzed and interpreted to identify the major hydrogeochemical processes. These results provided information on the current geochemical evolution of ground waters for two study sites within the Poços de Caldas Natural Analogue Project. The ground waters are a KFeSO 4F type, a highly unusual composition related to intense weathering of a hydrothermally altered and mineralized complex of phonolites. Tritium and stable isotope data indicate that ground waters are of meteoric origin and are not affected significantly by evaporation or water-rock interactions. Recharging ground waters at both study sites demonstrate water of less than about 35 years in age, whereas deeper, more evolved ground waters are below 1 TU but still contain in most cases detectable tritium. These deeper ground waters may be interpreted as being of 35 to 60 or more years in age, resulting mainly from an admixture of younger with older ground waters and/or indicating the influence of subsurface produced tritium. Geochemical processes involving water-rock-gas interactions have been modeled using ground water compositions, mineralogic data, ion plots and computations of speciation, non-thermodynamic mass balance and thermodynamic mass transfer. The geochemical reaction models can reproduce the water chemistry and mineral occurrences and they were validated by comparing the results of thermodynamic mass transfer calculations (using the PHREEQE program, Parkhurst et al., 1980). The results from the geochemical reaction models reveal that the dominant processes are production of CO 2 in the soil zone through aerobic decay of organic matter, dissolution of fluorite, calcite, K-feldspar, albite, chlorite and manganese oxides, oxidation of pyrite and sphalerite, and precipitation of ferric oxides, silica and kaolinite. Gibbsite precipitation can be modeled for the shallow (recharge) water chemistry at Morro do Ferro, consistent with known mineralogy. Recharge waters are undersaturated with respect to barite and discharging waters and deeper ground waters are saturated to supersaturated with respect to barite demonstrating a strong solubility control. Strontium isotope data demonstrate that sources other than calcium-bearing minerals are required to account for the dissolved strontium in the ground waters. These may include K-feldspar, smectite-chlorite mixed-layer clays and goyazite [SrAl 3(PO 4) 2(OH) 5·H 2O]

Thermodynamic properties of aqueous arsenic species and scorodite solubility

An internally consistent thermodynamic network for arsenic minerals and aqueous species is being developed based on a high quality starting point: arsenolite and arsenolite solubility. Current research is refining the properties of scorodite solubility as a function of temperature along with improved aqueous species stability constants and activity coefficients for ions and ion pairs based on potentiometric measurements of redox, pH, and conductivity for 5-90 °C. The second and third hydrolysis constants for arsenic acid have been calculated as a function of temperature and thermodynamic properties have been derived