Selective lithium extraction from brine via chemical reduction of iron phosphate with aqueous iron compounds

Abstract

Worldwide demand for lithium (Li) is surging due to increased production of Li-ion batteries to meet the needs for increasing numbers of electric vehicles and stationary energy storage systems. Conventional Li⁺ extraction from Li-bearing ores and brines has drawbacks of high chemical and energy inputs. In this work, chemical redox-driven processes were developed to selectively extract Li⁺ from brine meant to simulate a geothermal resource. Using additives that modify the redox potential of soluble iron compounds, ethylenediaminetetraacetic acid (EDTA) and citrate, the potential of the solution was shifted lower to drive reduction of a targeted solid electroactive material (FePO₄, FP). Li⁺ from simulated brine sources (with molar ratio Li⁺ : Na⁺ of 1 : 78) was extracted into the FP solid without additional energy inputs. The Li⁺ adsorption capacity for extraction with EDTA–Fe²⁺ solutions and citrate–Fe²⁺ solutions were 3.8 mmol Li⁺ g⁻¹ FP and 2.5 mmol Li⁺ g⁻¹ FP, respectively, and the selectivity factors for Li⁺ to Na⁺ for the two systems were 78 and 350, respectively. Similar extraction outcomes were achieved using a brine that more closely resembled the composition of geothermal fluids from the Salton Sea. This study more broadly provided insight into enhancing Li⁺ capture selectivity through modification of redox solution compositions.