| Abstract |
With a total of more than 95 s/s amorphous silica represents the major mineralogical component of the sediments at the bottom of the evaporation ponds at the geothermal field of Los Amfies, Mexico. The metals and non metals Fe, As, Cs, and Mn as further components are encountered' in decreasing abundance. ModiJcations of its primary, white or greyish color towards reddish or brownish tones can be explained by the presence of alguas and the input of terrestrial material. Observed seconabry processes of dissolution and redeposition of some mineral aggregates can be explained by changes of the saturation grade of the brine water. The programm PHREEQC was applied for the simulation of the geochemical behaviour of the geothennal brines within the evaporation ponds of the geothermalfield of Los Azufes, Mexico. The cooling of the fluids porn an input temperature of 90░C towards an average pond temperature of 40░C as well as fluid losses by,evaporation processes into the atmosphere were considered. Differences in the chemical composition of the inflowing and outflowing fluids can be attributed to the loss of approximately IO % of the water volume during its residence time within the evaporation pondr. Cooling eflect represents an insignificant factor for the precipitation or dissolution of the species as part of the fluid - solid system. The extraction of the metals and non metals j-om the sediments showed their variations in dissolution behaviour: The elements TI, Cs, Sr and Rb are very soluble, whereas lJ Ag, Cd, Ga and Hg become accumulated in the residual paction of the sediment. Ni, Cr, Bi and Mo get dissolvedfrom carbonate compounds. The major part of the metals and non metals get easily dissolved under neutral pH conditions, which are common in surface environments. Due to the elevated concentrations of Mo, Hg, Tl, and As, special treatment techniques will be required for the final deposition of the sediments in the future. |