Electrowinning is a very convenient and robust way to directly recover dissolved metals such as copper, silver, gold, nickel, cobalt, and tin from their aqueous states in a particular electrolyte.  Not surprising then when talking about metal recovery that we tend to focus most of our attention on those metals that we are interested in with the aim of recovering them from solution.  That is after all the objective of the metal recovery process.  What is less often talked about however are the impurities that can affect metal recovery with electrowinning.  This blog post will identify those impurities that are most detrimental and discuss their effect on the electrowinning of some commonly recovered metals from aqueous solutions. 

The electro-refining of copper is a multi-step process that starts with copper concentrate that is smelted to produce impure copper anodes, which are then electrorefined to produce LME Grade A copper cathode (+99.99%).  A simplified block flow diagram of copper refining is shown below.

Silver refining is a critical part of any precious metals refinery.  Often the higher value metals such as gold and the Platinum Group Metals (PGM’s) are associated with silver, which must be recovered separately as a by-product. 

A question that we hear from Clients every day is "Can I recover (copper - or other metals) from this?"  The material in question can be concentrated wastes, dilute effluents, ores, concentrates, residues, plating baths, bleed streams and so on.  It seems like a very easy and straightforward question to answer, and in some cases that is true.  In other cases, however, the answer is a bit more complicated requiring some additional information.  Let's take a closer look at the good, the bad, and the ugly when it comes to the common question "Can I recover (copper - or other metals) from this?"

The electrowinning of copper is an electrolytic process that uses electricity to recover dissolved copper from solution as copper plate, also known as ‘cathode’.

Cu²⁺_(aq) + 2e^- -->Cu_(s)        (E⁰ = +0.34V)

Copper easily dissolves in acids including sulphuric, nitric and hydrochloric. Recovering copper cathode from acidic sulphate solutions using electrowinning is a well-known and fairly straightforward process that has been in commercial use since the late 19th century.

Electrowinning is known as an electrolytic process because it involves electrodes submerged into an electrolyte.An electrolyte is simply a conductive solution formed by dissolving positively and negatively charged ions. 

Electrowinning is the process of ‘winning’ dissolved metals from solution by passing an electrical current through an electrolyte containing said metal.  The fundamentals of the electrowinning process have been discussed in a previous blog.  The relative ease of recovery depends on the electrochemical potential of the target metal relative to the Standard Hydrogen Electrode (SHE) which is defined by the following reaction: