Types of water used in mining & mineral processing
Water used for mining and mineral processing applications falls under two broad categories. Water removes mineral ores from the environment and processes the recovered minerals.
In removing mineral ores from the surroundings, water facilitates dust control. Integral water spray systems have spray nozzles used to materialize a water curtain around the mining area when operations are in progress. Clogged nozzles caused by scale formations and dirt particles can be disruptive, and inhibitors are added to this water line to prevent any scale formation.
In processing the recovered mineral ores, water in the form of an aqueous digestive medium is used for leaching to dissolve valuable minerals from the undesirable constituents in the ore. Under thermodynamic conditions of high temperature and pressure, there is a need for scale inhibitors to disrupt the formation of unwanted precipitation to allow for continuous operation.
Addressing problems faced in leaching & dissolving of valuable minerals
Some of these valuable minerals can include gold (carbon-in-pulp/carbon-in-leach; CIP/CIL processing), alumina (bauxite processing), copper (bacterial leaching), and sulfur (hot-water melting), to name a few.
A) Extraction of Gold (Carbon-in-pulp/Carbon-in-leach Processing)
CIP/CIL are continuous processes that involve the combination of activated carbon and cyanidation in agitation tanks to extract the precious metal of gold from its crude ores. The cyanidation process for extracting precious metals is used when the gold particles in the ore deposit are too fine or low in grade to extract or concentrate through gravitational and flotation methods. The aurocyanide ions in the solution then adsorb to the activated carbon flowing in countercurrent.
In the step of heap leaching, the aqueous solution of sodium cyanide and lime extracts the precious metal from its ore in the form of a soluble cyanide salt. The addition of lime maintains the oxidizing and alkaline conditions needed for cyanidation and prevents the formation of hydrogen cyanide gas. However, the setup of this alkaline environment increases the propensity of calcite scale formation.
The application of CrestoPro M475 inhibits the formation of calcium carbonate deposits at various points in the aqueous systems involved in the cyanidation process.
Apart from calcite formation in gold and precious metal mining and processing, different scale formations can also occur, depending on water quality and other determining factors. These factors can include pH, Total Dissolved Solids (TDS), calcium hardness, alkalinity, and existing concentrations of additional ion species in the water used in the aqueous solution. These other formations include gypsum, barite, and silica.
Acutely identifying potential scale formations from thorough water quality analysis can boost efficiency in resolving disruptions to operations by applying the correct type and dosage of scale inhibitors on site. In counteracting against the unwanted formations of gypsum (calcium sulfate scale formations), barite (barium sulfate scale), and silica scale, the application of CrestoPro™ M477, CrestoPro™ M478, and CrestoPro M479™ arrests the escalation of these issues respectively.
B) Extraction of Alumina (Bauxite Ore Processing/Bayer Process)
Bauxite ores are refined through the Bayer Process to extract alumina from its crude form. In alumina refineries, caustic solutions digest the raw bauxite at high temperatures to yield a slurry containing sodium aluminate, and red mud. With high heat and alkaline conditions, it encourages calcium carbonate scale formations.
The application of CrestoGuard™ 461 resolves the issues of calcium carbonate scaling in the pipelines, reducing the overhead costs assigned to manual cleaning and replacing the pipelines to ensure continuous operations.
Upon the filtration of the red mud, the pregnant liquor is cooled to facilitate the precipitation of alumina trihydrates, which are then filtered again and calcined to form the anhydrous alumina. With the removal of the alumina trihydrates, the spent liquor is then concentrated through the use of evaporators before re-use at the beginning of the circuit.
At the stage of concentration, silica, alumina, and caustic soda can easily exceed the threshold of precipitation and form insoluble aluminosilicate particles. These depositions hinder the efficiencies of heat exchangers and can lead to costly replacement of parts if severe damage is done over time.
The application of CrestoGuard™ CT2018/2019 allows for efficient dispersion and inhibits the formation of these insoluble depositions, allowing operations to run smoothly without unscheduled shutdowns for cleaning or replacement of parts.