Removal of lead and copper ions from geothermal brine at various temperatures and salinities using chemically crosslinked chitosan

Abstract

The control of mineral precipitation is a major challenge in several industry segments such as geothermal energy. In this study, the focus was on the prevention of lead and copper containing precipitations from geothermal fluids as frequently found at geothermal sites exploiting sedimentary basins such as from Rotliegend formations. A filter-material was applied to remove scale-forming heavy metal ions from the fluid and thus lowering the concentration of respective minerals below saturation. The filter-material was based on the cheap and abundant biopolymer chitosan and as such is easily available and environmentally harmless. The adsorption performance of lead and copper was investigated under various temperature and salinity conditions. The used synthetic solutions of the heavy metals contained also NaCl or CaCl2 as matrix electrolyte to take into account the salinity of geothermal fluids from sedimentary reservoirs. The obtained results from adsorption experiments showed that the concentration of lead and copper in the fluid could be lowered considerably in static batch tests as well as in dynamic flow-through tests over an extended time period. The adsorption rate increased towards higher temperatures when varied between 25 °C and 70 °C. However, despite chemical crosslinking the chitosan adsorption material exhibits a limited thermal stability with the adsorption performance deteriorating at elevated temperatures.