Study On Water-Rock Interaction Using Geochemical Reaction Modeling

Water-rock interaction is an attractive subject in earth sciences. Scientists have got a lot of thermodynamics and kinetics data of water-rock systems by means of experiments and investigations, which provide the basic theory and information to well understand water-rock interaction in the nature. However, these results are often obtained through geochemical analysis during reactions and this approach has many limitations. With the development of computer science, the study on rock-water interaction by geochemical modeling has been developed in recent years.Based on the theory of geochemical reaction equilibrium modeling, a kind of titration model was established in the thesis. The simulation software Phreeqc donated by USGS was used to study the mineral dissolution under different conditions such as pH, temperature, CO₂ partial pressure, ionic strength, etc. On the basis of data materials surveyed by others, groundwater-rock system in Zhuhai school zone was studied by geochemical reaction simulation.The results showed as follows. (1) Some minerals, such as aragonite, calcite, dolomite, were not saturated with groundwater. It indicated that limestone might be continued to dissolve. (2) The equilibrium of these systems was influenced by the factors including pH, temperature, CO₂ partial pressure, ionic strength and common-ion effect. It also indicated that temperature and CO₂ partial pressure have a relationship of mathematic functions with species. (3) The effect of acid rain was studied on water-rock interaction. It also showed ions such as Ca²⁺,NH₄⁺ would impact aragonite, calcite and dolomite dissolution equilibrium. (4) The simulation showed pH of groundwater would be less than 7, which might be a potential risk in the environment.