Institut za rudarstvo i metalurgiju Bor

leaching reagents in the gold mining because
of its high gold and silver recoveries
and relatively low costs of process [1].
And today, over 100 years later [2],
gold and silver are recovered using the
cyanide simple reactions 1 and 2:
4Au+8NaCN+O2+2H2O=
=4Na[Au(CN)2] +4NaOH..............(1)
4Ag+8NaCN+O2+2H2O=
=4Na[Ag(CN)2] +4NaOH.............(2)
Most cyanide leaching is carried out at
an alkaline pH between 10 and 11, depending
on individual concentrate characteristics
[3].
Concentration of cyanide solution is
also important in the leaching process with
concentration of NaCN ranging from
0.02% to 0.15%. Concentration of sodium
cyanide depends on precious metals content
and other ingredients, first of all copper
in sulphide concentrate.
Oxidant [4], first of all oxygen, has
also an important role in the leaching
process of precious metals in cyanide solution.
It has been proven that the dissolution
rate of precious metals in cyanide
solution is directly proportional to the
amount of present oxygen.
Mineralogical identification of concentrate
is used for defining the technological
flow sheet for concentrate [5]. Some alternative
leaching agents, namely thiourea,
have been tried due to the environmental
concerns, generally without economic success
[6].
EXPERIMENTS
Characterization of Raw Materials and
Treatment Methods
Investigations were carried out on sulphide
concentrate samples from the mine
"RUDNIK". Chemical analysis of concentrate
is given in Table 1.
Table 1. Chemical analysis of concentrate
Element Content, %
Cu 18.04
Fe 24.51
Pb 7.45
Zn 12.04
Bi 0.47
Ag (g/t) 895
According to the carried out X-ray –
structural analysis, the stage content of
concentrate is the following: ZnS, FeS2,
SiO2, PbS, CuFeS2.
For separation of non-ferrous and precious
metals from concentrate, the following
technological methods were used:
• Low temperature sulphatization for
the aim of transfer the sulphide forms
of metal into oxide forms
• Leaching of sulphatization products
with water for the aim of copper, iron
and zinc transfer into solution
• Cyanide leaching of Ag from
sulphatization product after the
recovery of non-ferrous metals.
• Thiourea leaching of Ag from
untreated concentrate.
Investigations were carried out with
100 g of concentrate per experiment. Tube
furnace for annealing was used in investigation
as well as the glass laboratory reactor
with heating lining and stirrer and
heater with automatic temperature regulation,
holes for charging and oxygen supply,
and the other necessary laboratory
equipment.
RESULTS AND DISCUSSION
Low Temperature Sulphatization Process
Low temperature sulphatization process
was carried out with the concentrated
sulphuric acid. By leaching with water,
after sulphatization, the following leaching
degree was realized (Table 2):
No 1,2010. 86
MINING ENGINEERING