Weathering pyrite

Due to the oxidation process, the pyrite quantity within a cell decreases with time, while the specific pyrite grain surface increases by the slow decrease in grain size during the decomposition. The increase of the specific surface is implemented as function of the pyrite quantity according to Eq. (7). 

Many reactions are so slow that it is impossible to describe them using equilibrium reactions (e.g. the weathering of quartz, or pyrite in the absence of microorganisms). However, it is often interesting to figure out to what extent these 

When flooding an abandoned mine processes of oxidation and reduction are of great importance. Due to the supply of oxygen, protons and sulfate are formed changing the chemistry of ground water fundamentally, e.g. mobilisation of metals as a result of the decrease of the pH value ( acidification ). 

Model the oxidation of pyrite with different oxygen supphes (0.0, 0.001, 0.005, 0.01, 0.05, 0.1, 0.3, 0.6, 1.0 mol), and show the changes graphically for the two major elements building up from pyrite dissolution as well as for the pH value of the ground water given in Table 30. 

In the data set used so far (WATEQ4F), NH4 is not included. Therefore, it has to be defined as an additional species. It can be done either directly in the data set or - like in this example - in the input file (see chapter 2.2.1.1). For that, NH4 has to be defined as a species and a respective reaction equation has to be included. The key words are the same as for their definition in the data set  

Anything in the input file always overwrites information in the database. Thus, 

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Iron in the feed concentrate is rejected either as unreacted pyrite mixed with elemental sulfur or as jarosites in the leach residue. The pyrite/sulfur mixtures said to be suitable for indefinite storage, but the well known environment effects caused by pyrite weathering are likely to make storage of this material a less than straightforward problem. Besides this, there are problems associated with the disposal of the leach residues from the pressure leach process. 

Other sources of river sulfate Include natural biogenic emissions to atmosphere delivered to land in rain (3%), votanism (8%) and pyrite weathering (11 %). 

Schwertmannite Acid pyrite-weathering waters, acid mine waters Ferrihydrite... 

In the following, an example for the definition of pyrite weathering rates is... 

As can be seen from Fig. 51, with increasing oxygen the pyrite weathering has a crucial influence on the concentrations of Fe2+ and S042, which increase from 0.001 mol/L to 1 mol/L 02 by about 3 orders of magnitude. The pH value drops significantly from 6.3 to 0.7. The resulting water is extremely acid. 

Fig. 51 Effects of pyrite weathering on the concentrations of Fe2+, SO.,2- and H+ in the absence and in the presence of calcite...

Sasaki K., Tsunekawa M., Ohtsuka T., and Konno H. (1998) The role of sulfur oxidizing bacteria Thiobacillus thioox-idans in pyrite weathering. Coll. Surf. 133, 269 - 278. 

Traverses were made across four copper-molybdenum deposits and soil gas was collected from holes drilled to a depth of 1.0-1.8 m. The soil air was analysed titrimetrically after absorption in an iodine solution. Control analyses were performed by mass spectrometry. The ore deposits, with widths of between 10-400 m, are associated with skams and granite porphyries. The thickness of the overburden is between 0.6-3 m. The ore minerals are principally chalcopyrite, molybdenite, chalcocite, bomite, galena, sphalerite, magnetite and pyrite. Weathering and secondary enrichment have affected the ores to a maximum depth of 95 m. 

In this chapter I will propose a kinetic estimate for the thermodynamics of reactions like Eq (lb). The solid phases listed in Table 1 may act as a reductant or an oxidant. One of the prominent geochemical electron donors is pyrite. From an estimate of global pyrite weathering of 36 Tgy"1 (Garrels et al., 1973) we may deduce an average electron flux on the land surface in the order of 0.02 mol m 2 y1. At redox boundaries in salt marshes and in lake sediments microbial sulfate reduction will intensify this electron cycling. Luther (Chapter 6, this volume) discusses the details of sulfide redox mechanisms. 

Hecht, H. K611ing, M. (accepted) Investigation of pyrite weathering processes in the vadose zone using optical oxygen sensors. Environmental Geology. 

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