Recycling Solutions - Thanatia: The Destiny of the Earth's Mineral Resources - page 440

Hydrometallurgy can, alternatively, be used for selective strong leaching either
with sulphuric or hydrochloric acids, or even cyanide or caustic soda. This process
may be used to strip metal coatings or for dissolving alloys. Using hydro-, pyro-
metallurgy or a combination of both to treat the recyclates is a matter of financial
viability and patenting. As occurs with conventional metallurgy, the separation of
metals from recyclates is also a question of chemistry, thermodynamics and kinetics
(Hayes, 2003).
Unfortunately, end-of-life recovery technology for most products is largely under-
developed. A critical case is that of products containing minor metals as explained
in the next section. Furthermore, there are no or very rough estimates about global
stocks and recycling rates of most metals and only a few estimates for the major
alloying metals at national level (Graedel et al., 2010).
14.6 Minor metals recovery
Hagelüken and Meskers (2010) consider minor metals as those that “have relative
low production or usage, which occur in low ore concentrations, are regarded as
rare, or are not traded at major public exchanges”. The Hague Centre for Strategic
Studies (HCSS - Kooroshy et al. (2009)), split them up into doping agents like
Ga;Li;Mo;Nb;Hf;Ta;W;Zr;REE, as well as Co;Re;Ge;In;Se;Te;As;Sb, and
Bi; and the precious metals PGM;Au and Ag. Important common features of these
metals are: first, most of them appear geologically related to major metals. Second,
they are used in many clean tech and high tech applications. Third, their intensive
industrial use began only thirty years ago, even in the case of historically precious
metals like gold and silver. This means that metals are subject to two core issues:
scarcity and a rocketing demand. There also exists a distinct lack of information
regarding quantities and e ciencies.
Minor metals require a thorough analysis as their extraction and their compo-
sition as dopant agents means that they have special properties which necessitate
complex recovery processes (either from the mine BoL or from old scrap EoL). They
also have issues relating to either absolute scarcity (Sec. 14.2) or supply shortages
as their demand escalates upwards.
14.6.1 Minor metals recovery fromBoL
Minor metals are secondary products released in the mining of other elements.
They occur in concentrations in the order of ppm, creating an entropic problem. As
already described in Chap. 8, copper mining produces the following byproducts: Co,
Mo, Re, As, Bi, Co, Se, Te, Au, Ag and PGM. Associated with the production
of tin are the rare earths, In, Ta and Nb whilst in the production of nickel there
are Cu, Co, Au and PGM. Aluminium meanwhile results in the production of Ga
and Ge and that of zinc and lead also leads to quantities of Ge, In, Se, Te, Bi,