The technique of recovering precious materials in electrical and electronic waste WEEE.

For some time, the system of waste management and recovery in Europe has started a fruitful recycle of post-consumer waste, albeit with different methods and results from country to country.

In particular, the most consolidated supply chains to date are those of paper, glass, metal, wood and plastic, from which enormous resources are obtained annually, in terms of secondary raw materials, which are used again for the realization of the products.

Just think of the aluminum or glass supply chain that have a very high recycling rate, allowing waste to be continuously reused in the production of articles , minimizing the use of natural raw materials.

In the world of waste there are also little developed recycling chains, which have potentially very high and promising growth numbers, from which a substantial contribution is expected to the recycling of precious chemical elements that, otherwise, we should extract from nature.

I refer to electrical and electronic waste, building materials, aggregates, and other materials that can contribute in an important way to improve the critical situation of raw materials on the international market.

Some metals, for example, are more difficult to find on the market and their cost has become almost prohibitive, at the same time, not having developed a recovery chain efficient, they are thrown in landfills.

A specific reference to the problem can be represented by WEEE waste, whose component recovery percentages are still quite limited, compared to the tons of waste that are thrown away every year every year in the world.

Within the WEEE waste we find extremely valuable raw materials, such as gold, silver, rare earths and other numerous metals which, although extremely precious, they are not easy to recover.

One way is to subject electrical and electronic waste, after their selection and grinding, to the so-called hydrometallurgy, a set of chemical and chemical-physical techniques, which allows the extraction from waste of precious minerals to be recovered.

What is the Hydrometallurgical process and how does it happen?

The Hydrometallurgical process deals with the liquid phase treatment of electrical and electronic waste, industrial waste or other types of waste, aimed at recovering the metals present.

The process can be divided into two stages, to simplify the process:

1. Leaching: consists of the dissolution of the waste to be treated through the use of a specific solution, allowing the dissolution of the solid element and the stability of the components.

2. Metal separation and purification: a solution containing metal ions and many other impurities is obtained from the leaching process. At this point it may be necessary to treat the solution in an appropriate manner (for example by means of a filtration to remove any suspended solids, or by varying some operating parameters, such as the temperature or pH of the solution itself), before proceeding to the subsequent phases of recovery of the metal.

The recovery and purification operations can be completed through the following steps:

• precipitation / crystallization

• ion exchange

• solvent extraction

• electrodeposition

For the extraction of the substances to be recovered, a solvent is used, through a phase called "liquid-liquid extraction", which is a process for which a liquid phase it is transferred to another liquid phase but not miscible with each other.

To carry out this operation an extractant is used, that is a molecule having complexing properties which, reacting according to various mechanisms with a substance dissolved in the aqueous phase, is able to pull it out.

These two phases, dissolving and extracting, constitute the organic phase, whose peculiarities are:

• the high selectivity which therefore allows the separation of metals with very similar properties

• possibility to treat industrial waste and residues

• high separation factors that allow to obtain products with an extremely high degree of purity

• simple, fl exible and easily automated systems

• systems with low environmental impact (solvents are continuously recycled and mainly at room temperature)

• low energy consumption

• possibility of treating matrices containing low concentrations of metals for low process costs.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.