Recovery of Minerals and Metals from Geothermal Effluent Brine

To me it is extremely exciting that geothermal power plants may also be able to supply valuable rare metals and minerals, such as lithium-ion, used for batteries in laptop computers and electric cars.

The following excerpt from a research paper on extracting metals from geothermal energy effluent is also linked in entirety to the html here: Recovering Metals from Geothermal Power Plant Effluent

Peace 2 All,

Yuya Joseph






DOE Report on Recovering Minerals / Metals from Geothermal Effluent

This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
March 9, 2005

Recovery of Minerals and Metals from Geothermal Fluids

William Bourcier, Lawrence Livermore National Laboratory
Mow Lin, Brookhaven National Laboratory
Gerald Nix, National Renewable Energy Laboratory


ABSTRACT

Geothermal fluids are potentially significant sources of valuable minerals and metals.
These fluids are water that is heated by the natural heat flow from the depths of the earth.
Hotter fluids, typically with temperatures greater than 120°C, are used to generate
electricity. Lower temperature fluids are directly used to supply thermal energy to
applications such as agriculture, aquaculture and space heating. The geothermal waters
have had intimate and lengthy contact with the layers of the earth’s crust that they flow
through, resulting in dissolution of minerals and metals from the rocks, and solution into
the hot water. These aqueous solutions can be processed to recover minerals and metals.
Potential products include silica, zinc, lithium, and other materials. Recovery of minerals
and metals from geothermal fluids can be viewed as “solution mining by nature”,
followed by application of established or new hydrometallurgical techniques for isolation
and purification. This paper discusses the opportunities, the processes, the challenges,
the current status, the economics and the potential for recovery of minerals and metals
from geothermal fluids.


INTRODUCTION

Geothermal fluids contain significant concentrations of potentially valuable mineral
resources. Although their mineral content was often considered more a nuisance than an
asset, there is now increasing interest in improving the economics of geothermal energy
by co-producing and marketing some of the dissolved constituents. Simple cost-effective
methods are needed to extract mineral byproducts from geothermal fluids. Useful
methods may have already been developed in the hydrometallurgical industry that could
be modified for use with geothermal fluids. Although the enrichment of target elements
in geothermal fluids is not as high as the enrichment in fluids commonly treated with
hydrometallurgical methods, the costs associated with resource extraction from
geothermal fluids are potentially low for several reasons:
•
Plant costs are split between power and mineral production. Geothermal power
plants already pump and process the fluids. Mineral extraction would consist of
an additional treatment step added to existing plant facilities;
•
There are no costs associated with mining and physical processing of the ore, and
no negative environmental impacts;
•
There are no costs associated with dissolution of ore minerals into an aqueous
phase because they are already in solution;
•
Geothermal systems process large volumes of water, commonly tens of millions
of gallons per day, so that the mass of mineral resource is large in spite of
relatively low concentrations.

This paper reports on previous and current research aimed at developing technologies for
resource extraction from geothermal fluids, and provides a summary of the targeted
mineral by-products, their potential value, and extraction methods being considered. It
also summarizes zinc and silica extraction work at CalEnergy’s Salton Sea, California
field, silica extraction work in New Zealand geothermal plants, and current work to
develop silica and other metals extraction at Dixie Valley, Nevada, and Mammoth Lakes,
California.

CHEMISTRY OF GEOTHERMAL SYSTEMS

Geothermal fluids are waters that percolate through and are heated by hot rocks. Most
geothermal systems are therefore located in active volcanic areas such as the Pacific Rim
and Iceland. Some are located in fractured areas that allow water circulation to great
depths where the fluids are heated by the earth’s natural heat, such as some Basin and
Range fields in Nevada and Utah in the U.S. The source of the water may be meteoric,
connate (filling the pores of the rocks), or a mixture, and in some cases a magmatic
component is present from de-volatilization of hot magma. Fluid compositions are
therefore variable. Acidities range from pH 5 to 9, and salinities from 1000 to over
300,000 ppm TDS. Most fluids have low oxidation states and may contain ferrous iron
and reduced sulfur.

The chemical components of geothermal fluids are determined by their source (e.g.
meteoric, seawater, magmatic), the rock types with which they have reacted along their
flowpath, the temperature of those interactions, and the chemistry of the fluid. Reservoir
processes such as mixing and boiling also impact fluid chemistry. The chemistry of fluids
sampled at the surface therefore reflect their chemical and physical history. Certain
elements may be especially indicative of their source. For example, lithium, cesium and
rubidium are often enriched in fluids hosted by silica-rich volcanic rocks. Silica
concentrations are generally controlled by strongly temperature dependent equilibration
with silica polymorphs. Systems with more saline chloride-rich fluids are enriched in
metals such as iron, zinc, and other base metals that form strong chloride complexes.
Such fluids can be derived from reactions with evaporite-rich sedimentary rocks, as in the
geothermal fluids from near the Salton Sea, or from seawater-basalt interactions.

Geothermal fluids are produced from subsurface reservoirs at depths commonly between
500 and 3000 meters. Their heat is extracted and used to generate power. The fluids are
then reinjected into the subsurface to replenish the fluid reservoir. Resource removal
optimally takes place after or near the end of the energy extraction process, but prior to
reinjection. The temperatures of reinjected fluids are commonly between 50 and 150 degrees C
and pressures at or slightly above steam saturation. In some cases, mineral extraction may
allow further energy extraction that, without treatment, would be uneconomic due to
scale formation. For example, the geothermal plants at Wairakei, New Zealand terminate
energy extraction as the fluids cool to below 130 degrees C because silica scaling becomes too
difficult to control (Brown, 2000). Silica extraction would allow additional energy

1. Fossil basalt-seawater geothermal systems are the hosts of “massive sulfide” base metal ore deposits that are major sources of the world’s lead, zinc, copper, silver, and barium.


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