Quantifying Dissolution and Precipitation
of Solid-Solutions in
Natural and Industrial Processes

The Group on Crystal Growth and Experimental Aqueous Geochemistry of the Department of Geology of the University of Oviedo is involved in a research network sponsored by the European Commission. The objective of the research to be performed by this network is the study of the dissolution and precipitation behaviour of solid solutions. The understanding of mineral-water reactions involving solid solutions and their quantification through rate equations is essential for the accurate chemical modelling of natural systems. A major result of this effort will be development of equations and algorithms that allow for the calculation of the dissolution and precipitation rates of natural solid solutions as a function of temperature, pressure and fluid composition. The resulting algorithms can be incorporated into comprehensive chemical mass-transfer algorithms to allow predictions of the fate and consequences of chemical transport during both natural and industrial processes.

The Participants

Economic Support

The project is supported by the European Commission in the framework of the programme Improving the Human Research Potential. The total cost of the project is 1,139,352 Euro (189.816.043 Ptas.), including the personnel costs for six young post-doctoral researchers (one for each group). From this total, 184,440 Euro (30.688.234 Ptas.) correspond to the group of the University of Oviedo.

Project Objectives

The approach to be adopted by this network is to focus in several distinct fluid-solid solution systems of particular relevance to natural and industrial problems:

  1. Characterisation of the dissolution rates of volcanic-basaltic glass
    Because of its widespread occurrence on the ocean floor and in volcanic terrains, its emission during volcanic eruptions, and its relatively rapid dissolution rate, basaltic glass plays a major role in the global flux and cycling of numerous metals and nutrients. Moreover, industrial produced glass has been proposed as a host for storing high level radioactive waste.
  2. Dissolution and precipitation of sulphate solid solutions as a function of temperature
    The project will begin on the system barite/celestite which forms massive scale deposits in wells of both hydrothermal energy plants and producing oil fields, resulting from the mixing of injected sulphate-rich seawater with barium rich pore fluids. Barite/celestite precipitation also controls the Ba/Sr budget in the oceans.
  3. Rates and mechanisms of metal-calcium carbonate solid solution precipitation and dissolution
    Crystallisation of metal-carbonate solid solutions represents a potentially significant metal-scavening process in aqueous phases. Divalent metals (M) including Cd, Zn, Co, Ni, Mn, and Pb can be removed from the aqueous solution by precipitation of (M,Ca)CO3 solid solutions or by growing an adherent solid solution layer on the carbonate surface. The dissolution and precipitation of such toxic metal bearing mineral phases can affect greatly the quality of fresh water found in rivers, lakes, and aquifers.
  4. Dissolution and precipitation of illite at sedimentary basin conditions
    The precipitation of this mineral during diagenesis lowers the permeability of petroleum reservoirs by up to two orders of magnitude, leading to a decreased production. Similarly such processes can also decrease the permeability of fresh water aquifers reducing drinking water supplies. Detailed knowledge of the dissolution and precipitation mechanisms of this mineral are therefore a prerequisite for accurate oil field reservoir and aquifer modelling.
  5. Determining the effect of leached layers and the presence of secondary mineral formation on amphibole dissolution
    Amphibole dissolution on the surface of the Earth is one of the main sources of plant nutrients such as Mg, Ca, K, and Fe in soils. The release of these cations to soils and their replacement by protons from groundwater can significantly enhance the acid neutralisation capacity of soils, and thus act as a buffer against the effects of acid rain. Long-term studies show that the release of these cations is more and more influenced by the presence of leached layers with time.
  6. Coupled dissolution/precipitation reactions
    Numerous reactions in natural systems occur by dissolution of a parent phase and the subsequent precipitation of a product phase on its surface. As the parent phase dissolves, the aqueous solution becomes supersaturated with respect to the product phase, which then precipitates on the surface of the parent phase. This precipitation can greatly enhance the dissolution rate of the parent phase and in turn can increase the growth rate of the product phase.
  7. Dissolution/precipitation in porous media
    Understanding the effects of porous media on dissolution/precipitation processes is essential to applying the results of the previous studies to natural systems. Because the fluid saturation state in a porous medium may vary with pore size due to the volume-dependent nucleation probability, the spatial distribution of dissolution/precipitation will depend on factors such as pore size distributions and flow rates.

Work Plan

The research to be performed by this network is interdisciplinary. Each research task outlined above will be directed by one of the teams (R) but other network teams will act as contributing partners. The structure of this overall work plan is given in the table bellow.

TASK
Toulouse
Oviedo
Reykjavik
Munster
Oslo
Bristol
A
C
 
R
 
 
C
B
 
C
C
C
 
R
C
C
R
C
C
 
 
D
R
 
 
 
C
C
E
 
 
C
R
C
C
F
 
C
 
R
 
C
G
C
C
 
C
R
 

16 de Septiembre de 2002