Nanofiltration and Membrane Distillation for Lithium Extraction from Geothermal Water
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Solution Overview
Problem
Current methods for extracting lithium, cesium, and rubidium ions from geothermal waters within geothermal power plants are inefficient, economically unviable, and environmentally harmful, as they often lead to unwanted chemical precipitation and require significant external energy and resources.
Innovation Solution
A method involving nanofiltration and membrane distillation is employed within the geothermal water circuit of a binary geothermal power plant. This method separates alkali metal ions from multivalent ions under high pressure and temperature conditions, avoiding chemical precipitation and utilizing existing plant resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical precipitation processes are used to separate divalent cations from brine, then separation is achieved, but heavy metals and radionuclides precipitate along with magnesium and calcium salts, creating environmental harm and additional processing complexity
Solution Approach 1:
The patent segments the separation process into distinct stages: first using nanofiltration to separate monovalent ions (Li+, Cs+, Rb+) from divalent ions (Mg2+, Ca2+, Ba2+), then using selective precipitation only for divalent ions. This segmentation prevents co-precipitation of heavy metals and radionuclides with magnesium and calcium salts, as the monovalent rare earth ions are already separated in the nanofiltration stage.
Solution Approach 2:
The patent introduces nanofiltration membranes as an intermediary separation mechanism between the brine and the precipitation process. These membranes act as a selective barrier that allows monovalent ions to pass through while retaining divalent ions, thereby preventing the direct contact between precipitation reagents and monovalent ions that would otherwise cause unwanted co-precipitation of heavy metals and radionuclides.
2Quantity of substance
If ion exchangers and liquid-liquid extraction methods are used to extract lithium from geothermal water, then lithium extraction is achieved, but a portion of the volume flow must be extracted from the thermal water cycle, disrupting power plant operations
Solution Approach 1:
The patent makes the nanofiltration system multi-functional by designing it to handle the entire geothermal water volume flow from the power plant. The system simultaneously performs: (1) separation of rare earth ions for extraction, (2) concentration of divalent ions for precipitation, and (3) production of purified water for reinjection. This eliminates the need to extract a separate portion of volume flow, as the same system handles all water streams.
Solution Approach 2:
The patent merges the lithium extraction process with the geothermal power plant's water cycle by integrating nanofiltration and precipitation units that process the full volume flow. The separated streams (monovalent ions, divalent ions, and purified water) are all utilized within the system, with purified water being reinjected into the reservoir, thereby maintaining operational continuity while enabling comprehensive rare earth extraction.
3Stability of the object's composition
If geothermal water is kept under pressure and at temperatures of ≥ 50 °C to avoid precipitation, then operational stability is maintained, but interaction with ion exchangers or ionic liquids becomes difficult
Solution Approach 1:
The patent changes the separation mechanism from chemical interaction (ion exchange or liquid-liquid extraction) to physical separation (nanofiltration based on ion size and charge). This parameter change in the separation mechanism allows the process to operate effectively at geothermal temperatures (≥ 50 °C) and pressures without requiring complex temperature control or pressure reduction, thereby maintaining both compositional stability and process feasibility.
4Quantity of substance
If conventional extraction methods are used, then lithium, cesium, and rubidium can be extracted, but the processes are economically unviable and require significant external energy and resources
Solution Approach 1:
The patent implements self-service by using the geothermal water's own properties (temperature, pressure, and ion composition) to drive the separation and concentration processes. The nanofiltration process utilizes the natural pressure of the geothermal water, and the selective precipitation leverages the temperature-dependent solubility of divalent ions. This eliminates or minimizes the need for external energy input and additional chemical resources, making the extraction economically viable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enables efficient, economical, and environmentally friendly extraction of lithium, cesium, and rubidium ions, minimizing disruptions to the geothermal power plant's operations and enhancing the economic viability of geothermal energy production.
Implementation Method 1
nanofiltration module (3) supplied geothermal water for the separation of alkali metal ions and other monovalent ions from multivalent ions under a pressure of 15 - 35 bar and a temperature of 50 °C - 80 °C
Implementation Method 2
precipitation unit (5a or 5b) for the precipitation of the remaining divalent alkaline earth ions
Implementation Method 3
membrane distillation (8) of the permeate heated in step H) under normal pressure and a temperature of 65 °C - 85 °C
Data Source
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AI summary
The present invention relates to a device and a method for extracting lithium ions and other rare alkali metal ions from geothermal water within a binary geothermal power plant by nanofiltration and membrane distillation.