Possible contribu.ons from the Solubility Data Project for arsenic and carbon dioxide environmental impacts mi.ga.on M. Clara F. Magalhães a and Jus2n Salminen b a Department of Chemistry and CICECO, University of Aveiro, Aveiro, Portugal b VTT Technical Research Centre of Finland, Finland
IUPAC mission v To advance the worldwide aspects of the chemical sciences and v To contribute to the application of chemistry in the service of Mankind. Promotes norms, values, ethics of science Advocates free exchange of scientific information and access of scientists Addresses global issues as a scientific, international, non-governmental, objective body 2
Foreword Environment is a dynamic system continuously changing All living beings interact with their environment changing it Living beings strive for survival and continuously adapt to their environment Environmental problems are mainly focused on the human beings welfare 3
Arsenic world problem Arsenic is becoming a major environmental problem Millions of people are being poisoned by water and food contaminated by arsenic Arsenic is mainly found in: primary and secondary minerals sediments soils aquatic systems (aquifers, soil solution,...) 4
Research on Arsenic shows Arsenic environmental impact has been a problem with no foreseen solution in the very near future Elemental environmental concern is not related to their presence in anomalous amounts but their availability to living beings Immobilization can occur through: precipitation of low-solubility salts adsorption on solids surfaces 5
Time ranges to attain equilibrium by different types of interactions D. L. Sparks, Environmental Soil Chemistry, 1995 6
Aqueous arsenic species of environmental significance H 3 AsO 4, H 2 AsO 4, HAsO 4 2, AsO 4 3 reduction HAsO 2, AsO 2 reduction (CH 3 R, H 2 S) Organic As Some examples: MeAsO(OH) 2, RAsO(OH) 2 (Me) 2 AsO(OH), (Me) 2 AsSSH (Me) 3 AsO (Me) 4 As + (Me) 3 As + CH 2 CH 2 OH RAs(OH) 2 7
Reliable solubility data of arsenic-containing substances must exist to promote arsenic immobilization under Earth surface oxidizing conditions Work to be done Reliable stability constants for aqueous arseniccontaining species must be available Aqueous arsenic-containing species have to be suggested and more research has to be done 8
Carbon dioxide in complex systems Ø Carbon dioxide as a useful reactive ingredient has increasingly gained interest in several process industries. These include buffered carbonate and alkaline systems that depend on the solubility and reactivity of the reactants. Ø Gaseous carbon dioxide is commonly used for ph control that facilitates dissolution and precipitation of carbonates. Ø Gaseous carbon dioxide is important for ph control in living beings. 9
There is a general trend to move to environmentally more friendly chemistry in industrial processes. Processes should be designed in new ways in order to reduce or completely stop using and generating hazardous substances. Advantages of using CO 2 Ø Safe reactant and natural product Ø ph control agent Ø Possibility to recycle CO 2 Ø New neat CO 2 based innovations replace more harmful and more expensive chemicals J. Salminen, P. Kobylin, Anne Ojala, Carbon Dioxide in Environmental Systems in Thermodynamics, Solubility and Environmental Issues, T. Letcher, Ed., Elsevier, IUPAC, 2007, pp. 189-203. J. Salminen and J. Prausnitz, Applications of Carbon Dioxide in Chemical Processes, in Developments and Applications in Solubility, T. Letcher, Ed., The Royal Society of Chemistry, IUPAC, Cambridge, UK, 2007, pp. 337-349.
Which data are needed? Ø Chemical equilibrium data are increasingly needed to interpret complex industrial and natural processes that contain dissolved CO 2, aqueous electrolytes, and solid precipitates. Ø Knowledge of molecular interactions, speciation and solubilities as well as chemical equilibria in reactive multiphase systems are needed to understand the solubility and speciation in natural systems, and to obtain reliable data for process design. 11
CO 2 in a closed system At specified temperature and liquid composition, the total pressure of the system is mainly determined by the concentration of non-dissociated dissolved CO 2 (aq) as is represented in the Henry s law. The non-dissociated CO 2 (aq) is in equilibrium with dissolved hydrogencarbonate and carbonate ions as well as other ionic species in the aqueous system, and also with solid phases. CO 2 (g) CO 2 (aq) CO 2 (aq) + H 2 O(l) H + (aq) + HCO 3 (aq) HCO 3 (aq) H + (aq) + CO 3 2 (aq) H 2 O(l) H + (aq) + HO (aq) 12
Speciation in a closed system Henry s law CO 2 (g) CO 2 (aq) log (concentration) 0.0-1.0-2.0 H(+) OH(-) K H = x CO p 2 CO ( aq) 2 = H 1 CO 2-3.0-4.0-5.0-6.0-7.0-8.0-9.0 CO2(aq) CO3(2-) HCO3(-) HCO2-H2O /MPa 700 600 500 400 300 3 Kiepe et al. Zawisza et al. Carroll et al. 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 ph 200 100 0 0 20 40 60 80 100 120 140 160 180 Temperature ( C)
Sparingly soluble M 2+ metal carbonates Solubility constant K = a (M 2+) a (CO 3 2-) M 2+ = Ca 2+, Zn 2+, Pb 2+, Cd 2+, Mg 2+ log log K sp 0 s0-3 -4-5 -6-7 -8-9 -10-11 -12-13 -14-15 ( ) MgCO 3, ( ) CaCO 3 (cal) ( ) ZnCO 3, ( ) CdCO 3 ( ) PbCO 3. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 CO 2 (g) CO 2 (aq) CO 2 (aq) + H 2 O(l) H + (aq) + HCO 3 (aq) HCO 3 (aq) H + (aq) + CO 3 2 (aq) MCO 3 (s) M 2+ (aq) + CO 3 2 (aq) H 2 O(l) H + (aq) + HO (aq) T / o C Temperature ( C)
Crystallization of solid phase in CO 2 -CaCO 3 -H 2 O system T P ph Saturation points of calcite ph of pure water at p(co 2 )=1 bar. ph 6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 J. Salminen, Chemical Thermodynamics of Aqueous Electrolyte Systems for Industrial and Environmental Applications, Doctoral thesis, Helsinki University of Technology, Espoo, Finland, 2004. 50 o C Equilibrium curve Equilib., Plummer and Busenberg (1982) 25 o C, calculated 50 o C, calculated Calculated saturation point of calcite 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 Ca 2+ / mmol/kg 25 o C
CO 2 acidification process ph and alkalinity are important measureable operational parameters which can be modelled as well Alkaline pulp T,P ph ph- PO bleaching stage control Ø CO 2 can be used to control ph and solubilities of M 2+ carbonates for example or set optimal ph Storage tank Ø Thermodynamic models based on critically evaluated data (IUPAC etc.) provide valuable information on solubility trends, speciation, ph to support safe operations CO 2 feed O 2, H 2 O 2, steam
Example of CO 2 utilization in industrial process Papermaking Ø Solid CaCO 3 is used as a filler in a office paper. Ø Recycled paper contains solid calcite that must be removed from the fibre surface. The calcite is precipitated back later in controlled manner Ø The dissolution and precipitation of calcite is controlled with ph by p(co 2 ) and common anion additive NaHCO 3. Ø Previously used sulfuric acid has been partially replaced by CO 2 gas. Good enviromental developments in the field: The water consumption in paper production has dropt from early days 1930: 350 m 3 / 1000 kg (paper) to 2010: 12 m 3 / 1000 kg (paper). That results higher ionic strenghts in process waters that CO 2 can partly tackle. J. Salminen, Thermodynamics (Papermaking), in McGraw-Hill Yearbook of Science and Technology, 2004, pp. 245-247. Koukkari P., Pajarre R., Pakarinen H., Salminen J.*, Ind. Eng. Chem. Res., 40 (2001) 5014-5020.
What can be done in IUPAC? Compilation and evaluation of the formation constants Compilation and evaluation of the solubility data Testing of the data using thermochemical modelling tools Interaction with stakeholders using the data Spread knowledge of solubility and its environmental importance Reports and recommendations 18
Acknowledgments The Portuguese Foundation for Science and Technology (FCT) for the financial research support of CICECO (Program Pest-PEst-/C/CTM/LA0011/2013) IUPAC project 2014-012-2-500 19