Brine mining

Lore & Background

Around 500 BC, the ancient Chinese dug hundreds of brine wells, some over 100 meters in depth. They drilled boreholes into large brine deposits beneath the earth's surface. Bamboo towers were erected, similar in style to modern-day oil derricks, using bamboo for ropes, casing, and derricks because it was salt resistant. Iron wedges hung from a bamboo cable tool attached to a lever on a platform atop the tower; two to three men jumped on and off the lever to pound the wedge into the ground to reach the brine.

Commercial brines include surface water (seawater and saline lakes) and groundwater (shallow brine beneath saline or dry lakes, and deep brines in sedimentary basins). Brine brought to the surface by geothermal energy wells often contains high concentrations of minerals but, as of 2015, is not used for commercial mineral extraction. Seawater has been used as a source of sea salt since prehistoric times, and more recently of magnesium and bromine. Saline lakes such as the Dead Sea and Great Salt Lake are appealing for mineral extraction; Lake Natron in East Africa is a potential source of sodium carbonate.

Deep brines in sedimentary basins have total dissolved solids (TDS) that vary from much less than seawater to ten times that of seawater. TDS generally increases with depth. Most deep brines are sodium chloride type, but calcium-to-sodium ratio usually increases with depth. The presence of high TDS is sometimes due to contact with salt beds, but more often thought to result from sediments acting as semi-permeable membranes during compaction.

Reader's Guide

Brine mining has been practiced for millennia, with ancient Chinese wells dating to around 500 BC demonstrating early engineering using bamboo derricks and iron wedges. Today, brines are a critical source of many industrial and strategic materials. Seawater provides salt, magnesium, and bromine; saline lakes like the Dead Sea yield potash and other salts. Shallow subsurface brines beneath dry lakes, such as Searles Lake in California, have supplied borax, potash, bromine, lithium, phosphate, soda ash, and sodium sulfate. As of 2015, subsurface brines yielded about half of the world's lithium production, with the largest operations at Salar de Atacama in Chile. The Salar de Uyuni in Bolivia is thought to contain the world's largest lithium resource, though no commercial extraction had taken place by 2015 other than a pilot plant. Geothermal brines have been tested for colloidal silica and zinc recovery, but sustained commercial-scale mineral recovery from geothermal brine had not been achieved as of 2015. Industrial brines from dairy, textile, leather, and oil industries also offer opportunities for resource recovery, though other chemicals and inhibitors may limit extraction. Brine mining supports waste minimization and resource recovery efforts, making it relevant to both historical and modern resource management.

Did You Know?

• Around 500 BC, ancient Chinese dug brine wells over 100 meters deep using bamboo derricks and iron wedges.
• As of 2015, subsurface brines yielded about half of the world's lithium production.
• The Dead Sea was estimated in 1996 to contain 2.05 million tons of potassium chloride, the largest brine reserve of potassium other than the ocean.
• Geothermal brines have been tested for colloidal silica recovery at Wairakei, New Zealand, and Mammoth Lakes, California, but as of 2015 no commercial production had been achieved.