Gravita
Exim Refining Plant use pyrometallurgical process
for Lead Refining, producing Lead with a minimum purity level of
99.97% from furnace tapped crude Lead. We supply refining kettle
furnaces of various capacities ranging from 5-100 tonnes per batch,
accompanied by high efficiency natural gas burners / furnace oil
burners, equipped with preheating arrangements. Emissions are
controlled by a flexible kettle hood, venting into a venturi type
wet scrubber, attached to an Induced Draft Fan along with a
chimney/stack arrangement.
Enclosure Hooding -
Refining Kettle Emissions Control
We
also provide additional equipment for automatic dross removal. On
demand, we supply a range of special fluxes designed to reduce dross
formation and increase process efficiency. The refining unit
complement is completed by the automatic Lead ingot-casting machine
(with Lead-Pump) having a production capacity of up to 25 tonnes/hr.
Our refining unit package is optimally configured for high
throughput with good emission control, as proven by the existing
installations in operation.
Recycled Lead Processing - Refining
The removal of impurities and other
metals from the crude Lead (S, Cu,Ni, As, Sb, Bi, Ag, Au, etc.). The
refining process is applied in several steps in kettles with
addition of specific agents alternatively smaller quantities are
processed by electrolytic refining.
A smelting plant stops at the stage of
the fusion-reduction plant, it will produce what is known as hard or
Antimonial Lead. If the plant is meant to produce soft Lead,
the crude Lead must undergo a refining process. The objective of the
refining process is to remove almost all copper (Cu), antimony (Sb),
arsenic (As) and tin (Sn), since soft Lead are not allowed to have
more than 10g per ton of these metals.
Pyrometallurgical Refining
Pyrometallurgical Refining is performed in liquid phase, which means that the
crude Lead must be melted to temperatures from 327ºC (Lead fusion
point) to 650ºC. As a general trend, the
process is performed in batches of 20 to 200 tons, according to the
refining plant capacity. The chemical concept behind the refining
process is the addition of specific reagents to the molten Lead at
proper temperatures. These reagents will then remove the unwanted
metals in a specific order as they are added selectively.
Copper (Cu) is the first element to be
removed with elementary Sulphur in a two phase procedure. In the
first step, almost all copper is removed as a copper sulfide (CuS)
skims when elementary Sulphur is added to the molten Lead at 450ºC.
The second step is meant to remove all remaining copper by adding
small amounts of elementary Sulphur to the molten Lead at 330ºC until
no reaction takes place anymore. Tin (Sn) is next removed BY either
chlorine (Cl2) or ammonium chloride (NH4Cl) oxidation. The addition
of chlorine to the molten Lead at 500ºC produces tin chloride
(SnCl2) skims which are mechanically removed. Although this is the
current method for tin removal, its inconvenient is the parallel
removal of small amounts of antimony (Sb) and arsenic (As) by
oxidation.
Lead Ingot Casting Machine
Arsenic (As) and antimony (Sb) are
selectively removed by oxidation with either air enriched with
oxygen (O2) or a mixture of sodium nitrate (NaNO3) and sodium
hydroxide (NaOH). The temperature of the molten Lead is raised to
550ºC and a flow of O2 enriched air is bubbled into it. The reaction
is extremely exothermic and the temperature easily reaches 650ºC.
Those skims are a mixture of oxides (25% Sb, 10% As and 65% Pb).
Silver (Ag) come next and its removal
is carried out by the Parkes Process, which makes use of the
preferential solubility of silver in molten zinc (Zn) instead of
molten Lead (Pb). Therefore, metallic zinc (Zn) is added to the
molten Lead at 470ºC and the mix is allowed to cool to325ºC. A
silver –Lead zinc alloy separates and forms a crust on the surface.
The crust is removed and the zinc separated from the silver by
vacuum distillation. The crude silver is further refined using
oxygen to produce fine silver. The excess of zinc is removed from
the de-silvered Lead by vacuum distillation and then by Sodium
hydroxide (NaOH).
For
an overview of our entire range of available services from,
feasibility studies to turnkey Plant, retrofitting and
modernisation of existing units for capacity expansion to pollution
control solutions reengineering, see our services & turnkey projects
section. Contact Us with your requirements for a customised
equipment, solutions and services package.