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Wastewater treatment and water recycling

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Jenni Kivi

on 14 October 2014

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Transcript of Wastewater treatment and water recycling

Wastewater treatment and water recycling
WASTEWATER TREATMENT
TECHNOLOGIES AND
WATER RECYCLING
IN MINING AND
MINERAL EXTRACTION PROCESSES
Case:
Water and solution recycling in the Canadian mineral industry
Methods for treatment of recycle water
The aim of the thesis
Contents of the thesis
The
reasons
for water use in mineral extraction processes
The
reagents
used and the
wastes
formed in the processing of ore and minerals
Wastewater
treatment
technologies for different mineral industry wastewaters
The basic
chemistry
behind the processes
The
motives for recycling
of process waters
The
best available techniques
considering mining activities
in mining and mineral extraction processes
Master's Thesis
Jenni Kivi

Aalto University
School of Chemical Technology
Degree Programme of Materials Science and Engineering

A literature survey
To consider the
possibilities
in reasonable and efficient water usage and high water recycling rate in mining and mineral processing industry.
To
collect background information
for the future projects and development of wastewater management technologies and water recycling in mining and mineral extraction processes.
Szyplinska, 2012.
Water intensities of key minerals and metals
Effects of using
recycled water
in sulfide and non-sulfide flotation
Rao and Finch, 1989.
Rao and Finch, 1989.
The motives for the
recycling of water
Both economic and environmental reasons
Mineral processing plants may use a large proportion of the local water resources
Reduced availability of water for others
Shortage of water
in hot arid or semi-arid areas
On the other hand, too much water in e.g. Scandinavia
The
production and transportation
of fresh water are usually expensive
.
Recycling can lead to
savings
in water, energy and reagent consumption
The
impurities
, such as heavy metals, metal ions and residual reagents in the flotation wastewater are one more reason to aim for
directly re-using the water in the process instead of transporting it to the disposal area
.
...motives continued
Sulfide flotation
Non-sulfide flotation
Final remarks
As mineral production continues to be necessary for economic development, the
recycling and re-use
of mining and mineral-processing wastes need to be developed now and in the future.
Water is getting more expensive to gain and recover. At the moment,
pricing of water
is distorted as governments want water to be as cheap as possible.
The pricing should prevent misuse.
Purifying recycled process waters only to a suitable level
concerning the process
(not to a level needed when water is discharged back to the environment) could lead to
cost-savings
.
The amount of make-up water is thus also decreased.
What has been done and noticed:
No problems in
gravity and magnetic concentration
circuits.
Recycling in
simple flotation
circuits is well developed.
The most serious problems are in
multi-stage
circuits using selective flotation.
In the
cyanide gold industry
, recycling is limited due to the build-up of complex chemical compounds and a high concentration of sulfates.
In the
uranium
plants using acid leaching, recycling is not practiced because of the impurities and incompatibility with the process. In carbonate leach plants, alkaline leach solutions are recycled.
Mine water is recycled in the grinding-thickening circuit.
Joe, 1984; Joe and Pickett, 1974; Ritcey, 1989.
Example:
recycling in different mills
in Canada
Precipitation
(alkaline earth and heavy metal ions)
Adsorption
on active carbon or coal (organics)
on mineral slimes (metal ions, some organics)
on bentonite clay (metal ions, amines)
at liguid-gas interface (surface-active organics)
Ion exchange
, IX (ionic species)
Dissolved air flotation
,
DAF
(ions, ultrafine particles, precipitates, micro-organisms, oils, proteins)
Membranes
Reverse osmosis, RO (electrolytes: dissolved salts, organics, colloidal solids)
Electrodialysis (electrolytes)
Oxidation
by e.g. ozone (organics)
Biological oxidation
(degradable organics)
Atmospheric

freezing
(electro-lytes and organics)
(In brackets: what is removed)
Hoag and Albern, 1977
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