Converting Minerals to Metals - Mining and the Environment: From Ore to Metal - page 283

Management of Waste Streams

Spent ore consists of the material remaining in either dump or heap leach piles when
leaching ceases. Spent ore from heap or dump leaching may contain residual lixiviant and
other constituents of the ore (a lixiviant is a solution used in hydrometallurgy to selectively
extract the desired metal from the ore). Wastes from vat leaching operations are commonly
referred to as tailings. Another consideration is that heap leach piles may periodically be
used as a disposal area since most spills that occur at the mine site may be ore excavated
and transported to the heap for leaching. Also, sludge generated at the solvent extraction
facility may be deposited on the heap for leaching of residual metals.
SX/EW sludge is the semi-solid gelatinous material (i.e. soft mud, slime, slush, or mire)
that can accumulate in SX/EW tanks. Sludge is in the form of colloids of suspended material
(mostly silt or clay, usually less than 5 angstroms in size) that cannot be easily settled or filtered.
Sludge accumulated on the bottom of the tanks over time needs to be removed. Sludge volume
and its method for disposal, is relevant; it may be deposited on the heap for additional leaching.
The solvent extraction process specifically generates a sludge termed 'crud' or 'gunk'
in the copper industry. This sludge consists of a solid stabilized emulsion of organic and
aqueous solutions from solvent extraction. It is located at the organic/aqueous inter-
face in the settlers and is periodically removed from the system, and centrifuged or oth-
erwise treated to remove the organic constituents. The aqueous solutions and the solids
are disposed of and the organics are returned to the solvent extraction circuit for reuse.
Depending on the characteristics of the ore, SX/EW sludge may contain base or precious
metals in quantities sufficient for recovery.
Spent electrolyte is generated during electrowinning activities. Historically, the electro-
lyte went through a stripping step and was subsequently discharged to a tailings pond.
Today, this effluent is recycled to reduce the costs associated with the electrolytic acids
used in these operations.

S-Furnace

CL-Furnace

C-Furnace

Anode Furnace

CASE 6.8
Smelting Technology for the Twenty-fi rst Century

of matte and slag formed in the S-Furnace fl ows continu-
ously to the CL-Furnace, where the denser copper matte
separates from the discard slag. The matte is then siphoned
to the C-Furnace, to be continuously converted to blister
copper and C-slag. The latter is water granulated, dried, and
recycled to the S-Furnace, while blister copper is siphoned
continuously from the C-Furnace to the Anode Furnace.

Material fl ow from one furnace to another is continu-
ous and enclosed greatly reducing fugitive emissions. Sludge
from the wastewater treatment plant is recycled to the
S-Furnace with granulated slag being the fi nal outlet of
most gangue material and impurities.

The graphic for this case schematically illustrates the
Mitsubishi Process, showing the sequential smelting, slag
cleaning, and converting stages and the continuous delivery
of blister copper to the anode furnaces.
Three launder-connected furnaces are used: a circular
Smelting (S) Furnace, an elliptical Slag Cleaning (CL)
Furnace, and a circular Converting (C) Furnace. The mixture