Overview
There are a number of
Hydrometallurgical
approaches to refine or purify metals using wet
Chemical Reduction Methods.
The use of Strong caustic PH Base stripping baths is one common process.
Solvent Extraction
methods to achieve Absorption or Adsorption are also employed in various applications.
One of the most commonly used methods encountered involves the use of
acids
to segregate metal complexes
by dissolving mixed metals into solution and
selectively
recovering each individual metal.
Residual Materials
It is generally assumed that any metals or materials of significant value would have been eliminated by source separation or
salvaged by treasure hunters who cherry pick any "low hanging fruit".
We therefore take for granted that any material entering the Recovery 2.0 system is the less desirable
residual materials that can not be easily recycled by manual or mechanical means.
This leads us to a bottoms up approach to base our recovery methods on a lowest common denominator default
for the ultimate treatment of disposition of residues.
Acid Leaching
When you encounter elements that are difficult or impossible to segregate with manual or mechanical methods,
you need to use alternative processes such as
Pyrometallurgy
or hydrometallurgy.
The extraction of metals from ore concentrates, metal residues and complex metals matrix materials
may be achieved by an
Acid Leaching
process.
By utilizing any combination of acids to dissolve the metal complexes into ionic solutions
the segregation and purification is possible.
A wide variety of acids are commonly encountered that are generated from industrial waste streams, but the most common are
Hydrochloric
(HCl),
Sulfuric
(H2SO4),
Nitric
(HNO3)
Acids.
Controlled in-vessel leaching, dissolving metals into an acid solution is a highly
exothermic reaction.
Harnessing energy from this redox reaction may be achieved in several ways. One method is with the use of a
Harvesting Module
that captures the heat energy in a
Thermal Energy Generator.
Further advancements in material sciences may allow for the conversion of the Leaching system into duel purpose
metal refining and energy harvesting
Electrolytic cells.
The movement of the metal saturated ionic solutions between the leaching reactor, storage buffers and the displacement reactors
provides the opportunity for the location of a highly tuned, low velocity Magneto Hydro Dynamic (MHD)
harvester.
Acid Regeneration
The treatment and processing of
Acid Wastes
or material generated from
Acid Leaching
operations are contained in a closed loop system to insure the regeneration
on a Mass Balance
Equilibrium
basis.
A common example of closed loop acid recycling is by capturing the fumes generated by nitric acid leaching
and sparging them through a water column creating a dilute nitric acid.
This regenerated acid may be stored and cycled back into the leaching reactor as required,
conserving the need for a fresh supply of acid and water.
If a more concentrated acid is required the distillation of nitric acid with a boiling point of 83 °C
may effectively separate the acid from the water.
Rinse Water
The leaching process generates voluminous amounts of Rinse Water or wash water into a
wastewater
cycle.
Wastewater management is an integral part of a
regenerative
hydrometallurgy process.
Metal Recovery
Purified Metal or other desired products may be recovered from the ionic acid solutions.
The typical recovery methods used are precipitation, direct displacement and
Electrolysis
The recovery of metal residues and mixed metal complexes may be desirable as items for processing with hydrometallurgy methods.
A wet chemical approach may be an efficient option to achieve the recovery of those items that are
difficult or impossible to segregate manually or mechanically.
Highly mixed materials such as Recovered
Electronic Components
accumulated from Depopulating Circuit Boards contain a vast number of combinations of different types of precious and base metals.
In order to efficiently recover the spectrum metals contained within these electronics mixes,
following a systematic
sequence
may be the best approach to ensure the extraction of all the values contained.
Recent advancements in technology have allowed for the real-time
identification
of materials as they flow through the recovery process.
Silver Recovery
Scrap materials such as ornamental silver plated items or
small electronic switches or contacts that are permanently affixed to copper buss bars,
or lead free solders that contain small quantities of silver,
are difficult or impossible to manually or mechanically segregate.
Dissolving these types of scrap materials in a solution such as Nitric acid is one approach that may be used to achieve
silver separation and recovery.
Once the acid solution is saturated with metals, the ionic silver nitrate may be displaced out of the solution
and recovered as metallic silver with the addition of excess metallic copper.
Real Time
Analytics
will allow the immediate determination of the quantity of copper required to complete the displacement reaction.
An alternative method to precipitate the silver nitrate out of solution is with the addition of hydrochloric acid.
The silver will be converted into a silver chloride which then may be oxidized and the silver oxide may then be reduced
into metallic silver. This is a multi-stage process that leaves you with multiple acid complexes to deal with.
Copper Recovery
Continuing on with the nitric acid solution, once the silver has been removed, the remaining copper nitrate may be
reduced by the direct displacement with iron. The quantity of iron required may be determined with Real Time
Analytics.
Tin Recovery
Tin
(Sn)
may be recovered from circuit board trimmings and
depopulated
circuit board scrap, tin platted coppers and lead free solder scraps.
In nitric acid, Tin reacts to form a
Tin Oxide
(SnO2) precipitate.
The recovery of Tin is a source for the
Strategic
Use of Tin.
Steel Recovery
The Iron that remains as a Ferric nitrate saturated solution may be directly thermally reduced.
The reduced
iron
may be recovered as the nitrogen dioxide is distilled off, contained, captured and regenerated into
a fresh batch of
nitric acid.
The Acid House
The Hydrometallurgy processing unit is housed in a section of the Recovery 2.0 operation
known as The Acid House.
Each
leach line
operates as a restricted circuit, maintaining control of its own fluid inputs or outputs.
All emissions are managed for the safety of overflow or spillage and each circuit operates as a
regenerative
loop which contains fumes, vapors, air and water or other liquid flows.
Each leach line
circuit
is wrapped in its own cell envelope, which may be considered as operating inside a fume hood,
where the cell environment may be managed, recirculated and controlled.
In addition, all of the operating cells are combined into an umbrella envelope that we refer to as
The Acid House which ensures the containment, safety and management of the enclosed environment.
The Acid House maintains full filter, scrubber, storage and spill contingency management and monitoring systems.
Within the acid house, isolated rooms are established for the operations of nitric, chlorine, aqua regia and sulfuric loops.
Each of the acid house rooms maintain independent acid gas regeneration systems.
In addition to the wet chemical hydrometallurgical leaching modules, there exist melt shops that facilitate
the molten electrolysis and aqueous alkaline electrolysis operations
that also collect and contain the acidic and non-acidic off gases.
