Laboratory Investigations to Optimize Tungsten Mobilization Under Geothermal Reservoir Conditions
Máté OSVALD, János SZANYI, Tamás MEDGYES, Balázs KÓBOR
[University of Szeged, Hungary]
In a properly established engineered geothermal system (EGS) residence time and contact surface have crucial importance. In any scenario, during such utilizations of geothermal energy fluid injected into wells will react with the reservoir. Whether natural and artificial fractures are going to clog or propagate over time is mostly dependent on the characteristic of the reservoir. According to our hypothesis, tested in the EU H2020 project “CHPM2030”, an EGS system could be established in a way that fluid can react with, and dissolve nearby metal enrichments. Tungsten has long been identified as one of the most critical elements in terms of raw material accessibility in the EU, therefore the possibility of mobilizing tungsten from a geothermal reservoir was investigated in this study. A custom-built flow-through reactor was used in our laboratory work to most precisely create the conditions of an EGS. There, scheelite and ferberite, the two most abundant tungsten minerals were crushed and reacted with different fluids with different physical parameters to obtain data about tungsten mobilization under geothermal reservoir conditions. In this research, deionized water, acetic acid, sodium hydroxide, and the mixture of hydrochloric acid and nitric acid were tested as possible leaching agents. All reactions were conducted at around 250 bars pressure, which corresponds to the pressure of the hypothesized EGS. The reactor was heated up to 200°C, 250°C and 300°C temperature while 0.5 ml/min – 1.0 ml/min flowrates were maintained by a HPLC pump. At the exit of the reactor a slow but continuous flow could be observed, and samples collected. The leachate samples were analyzed with single element ICP-OES. Concentration of leaching agents were kept relatively low (around 0.1 M), to maintain possible future applicability by limiting the potential environmental and social impact of pilot scale implementations. In situ leaching yielded tungsten concentrations of 1–3074 mg/L in the leachates, with sodium hydroxide being the most effective in mobilizing tungsten from the mixture of ferberite and scheelite.
|        Topic: Geochemistry||Paper Number: 14152|