Thermodynamics of Mineral Resources - Thanatia: The Destiny of the Earth's Mineral Resources - page 254

Each aggregate is characterised by two different properties: a cohesion (binding)
energy, represented by its formation enthalpy and a formation entropy or an entropy
of mixing. The four stages implicated in the formation of the mineral deposit are
outlined as follows:

Stage I: Molecular formation: Atoms (g) ! Molecule (g)+ H,

S

Stage II: Solidification: Molecule (g) ! Molecule (s)+ H, S

Stage III: Mineralisation and rock formation: Solid 1 + Solid 2 !

Mineral+ H, S

Stage IV: Deposit formation: % Mineral + Rocks ! Mineral deposit

+ H, S

Once the deposit is mined, the process reverts. The mineral must be separated
from its gangue and concentrated. Then it is smelted and refined. These processes
consist of a number of physicochemical separations plus a series of chemical and/or
electrochemical reactions:

Stage Va: Mining: % Mineral deposit ! Mineral + Rocks (gangue)+

H, S

Stage Vb: Beneficiation: % diluted Mineral ! concentrated Mineral

+ H, S

Stage VIa: Mineral smelting (chemical reduction): % concentrated Mi-

neral ! impure Metal + H, S

Stage VIb: Metal separation and refining (electrochemical and separa-

tion processes): % impure Metal ! Metal + impurities +
H, S

9.2.1 Stage I: molecular formation

The energy required to form one mole of a compound from its elements (at 1 bar
and 298.15 K) is specified by its formation enthalpy.
So, the formation of hydrogen fluoride, for instance, requires 563 kJ/mol, which
is the amount of energy released when a mole of HF is formed from its already
dissociated gaseous atoms:

H(g) + F(g) ! HF(g) -563 kJ/mol
This enthalpy allows for the measurement of the energy needed for atomic sep-
aration. As can be seen from the following example, the bond HF is more stable
than the corresponding H H or F F bonds.

2H(g) ! H 2 (g) -436 kJ/mol
2F(g) ! F 2 (g) -153 kJ/mol