Heat and Mineral Mining by adding CO2 to Deep Groundwater
Arab, Alireza; Merkel, Broder
Technische Universität Bergakademie Freiberg, Germany
Geothermal waters are potentially significant sources of valuable elements and metals. Deep groundwater has lengthy contact with the layers of the earth’s crust resulting in the dissolution of minerals and metals from formation rocks into the geothermal hot water. These aqueous solutions can be processed to recover these elements and metals. However, in many cases, the concentration of the elements and metals may be too low to be economically considered for extraction. Addition of CO2 to the geothermal water can enhance the dissolution of rock and enrich the geothermal water.
For this reason, the interactions of water and CO2 under reservoir conditions were investigated kinetically using reservoir rock from the Molasse basin and also carbonatite rock from the Delitzsch, Germany. The solutions of all experiments were analyzed for their chemical composition (by means of ICP-MS and IC), as well as the content of the dissolved CO2 in the water. In addition to the water chemistry analyses, a microscopic examination of solid material surfaces before and after the experiments was carried out on the sample material using SEM.
Results show that adding CO2 to the geothermal water can cause the dissolution of a wide range of elements and metals. Also, this favored dissolution of rock could lead to improvement of the permeability in low permeable formations. Economic production of minerals, along with the production of electricity and heat from geothermal power plants can potentially improve the economic and production benefits of geothermal energy projects, making them more cost-effective at a wider range of locations. Elements such as lithium, zinc manganese, silica, sulfur, strontium, rubidium, potassium, magnesium, lead, copper, boron, silver, tungsten, gold, cesium, barium can be extracted from geothermal fluid to obtain marketable by-products.
Minerals related to some of the aforementioned elements are a major source of scaling and corrosion which has severe negative impacts on geothermal energy production. Moreover, this suggested approach could eventually become a safer and resource-conserving alternative to current techniques especially due to the fact that above ground energy production is not interrupted while CO2 is being added. This and the positive CO2 storage as by-effect (Carbon Capture, Utilization and Storage) and avoiding the formation of tailings are all benefits of the investigated approach.