The Speciation Of Chlorine And Nitrogen In Hydrothermal Fluids

Hydrothermal fluids play a key role in materials'cycling and transportation between Earth's interior and surface,and have a profound effect on the formation and evolution of Earth's atmosphere and ocean.Volatiles tend to concentrate in hydrothermal fluids,and their speciation in hydrothermal fluids has a significant effect on their distribution and isotope fractionation between fluids and coexisting phases(such as minerals or silicate melts).Our work simulate the high temperature and high pressure conditions with a hydrothermal diamond anvil cell and in-situ methods to study(1)the ionization behavior of KCl in hydrothermal fluids;and(2)the conversion between N2 and NH3,based on which explores the speciation of nitrogen and chlorine in hydrothermal fluids.The results are as follows:(1)The speciation of Cl is obtained by the ionization constant of KCI hydrothermal solutions at high temperature.The ionization constant is calculated by measuring the electrical conductivity of the KCI solution.In this paper,a hydrothermal diamond anvil cell is used as a conductance cell and fluid chamber,with an impedance analyzer in suit measuring the electrical conductivity.We have developed a new method for acquiring electrical conductivity of hydrothermal fluids under pressure.Compared with the traditional method(800?,0.4 GPa),our technique can greatly extend the pressure range.Our preliminary results are measured to 600? and 0.8 GPa,which are consistent with literature data acquired with the conventional method,but the new method has great potential for working in a much broader pressure range.Our results show that the electrical conductivities of 0.1 mol/kg KCI solution can reach several S/m.Besides,with the experimental temperature increases,the ionization constant of KCI solution becomes smaller,that is,it is more in the form of KCI molecule.(2)The speciation of N is obtained with a hydrothermal diamond anvil cell and in-suit Raman spectroscopy.When NH2OH solution is used as the starting material,upon heating the solution decomposed stoichiometrically to produce equivalent amount of NH3 and N2.N2 and NH3 are only detected N species at high temperature.When Pt powder was added as a catalyst,we observed the conversion of NH3 to N2 and the appearance of H2.Compared the equilibrium constant of this reaction with the quenching method and DEW model calculations,it was found that the results of the quenching experiment may not truly reflects the equilibrium speciation at experimental conditions.For hydroxylamine hydrochloride solution as the starting material,N2 is the only detectable N species and NH3 can't be detected.With temperature increases,and the conversion of NH4+ to N2 occurred,but the results need to be further explored.