Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1999-03-25
2000-10-31
Hruskoci, Peter A.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210724, 210738, 210912, 423140, 423142, 423594, C02F 164
Patent
active
061397539
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to precipitation processes for the remediation of acidic waste and drainage waters comprising metal and/or metalloid ions such as ions selected from (but not restricted to) the group consisting of copper, zinc, lead, mercury, cadmium, iron, arsenic, barium, selenium, silver, chromium, aluminium, manganese, nickel, cobalt, uranium and antimony.
In particular the invention relates to the remediation of acidic waste water comprising iron ions and sulfate ions, as well as other undesirable metal or metalloid species. Such waters are frequently formed as a result of the oxidation and leaching of sulfide minerals during and after mining operations, and are referred to as acid mine drainage.
Significant quantities of acid mine drainage are associated with many former and current mining operations such as the Berkeley Pit in Butte, Mont. USA. The problems caused by acid mine drainage include: to flow to areas producing contamination with toxic elements being labile or only loosely bound by adsorption oxidation to sulfuric acid purposes and contaminated water, e.g. copper and zinc. Approximately 8000 lbs (3600 Kilograms) of copper and 20,000 lbs (9000 Kilograms) zinc enter the Berkeley Pit each day.
A wide variety of methods have been proposed for the remediation of acid waste drainage.
In-situ mitigation is a method whereby limestone placements are put down to collect surface run-off and funnel it into waste rock dumps. Such a method is described in SITE 94, p. 374, presented by the University of South Carolina. [The publication SITE 94 refers to the U.S. EPA Superfund Innovative Technology Evaluation Program, Technology Profiles, Seventh Edition 1994. This document is issued by the Risk Reduction Engineering Laboratory Office of Research and Development, U.S. EPA Cincinnati, Ohio, 45268, USA.] Acidic material is capped with an impermeable layer to divert water from the acid cores. This method relies on the existence of sufficient rainfall to produce seepage or drainage that continually contacts the limestone. The method has limited efficiency for remediation (as judged by the acidity of treated versus untreated areas) and is weather dependent.
Wet-lands based treatment has also been considered. This method uses a man-made wet-land ecosystem to remove heavy metals and is described in SITE 94, p. 164 (Colorado Department of Public Health and Environment). This method is not able to recover useful metals from the acid mine drainage and removal efficiencies are generally less than for chemical precipitation processes.
Another method described in SITE 94, p. 56 (Dynaphore Inc.) involves adsorption followed by pumping or drainage through an open-celled cellulose sponge containing amine-functional polymers with selective affinity for aqueous heavy metals in both cationic and anionic form. This method (in common with other methods based on absorbent or adsorbent material) has limited efficiency for the removal of some metal ions from a complex mixture and for anions such as sulfate. It is characterised by high capital costs and by the generation of relatively dilute strip liquor.
SITE 94 at p. 304 describes a method involving precipitation plus adsorption in which the pH of the waste stream is adjusted to 9-10 (under standard atmospheric conditions) followed by pumping/drainage through a column containing adsorbent ferrihydrite applied to the surface of an inert substrate such as sand. This method has limited efficiency for the removal of sulfate anions and generates relatively dilute strip liquor. For waste streams containing relatively high levels of ferrous ions such as acid mine drainage from the Berkeley Pit, the adjustment under oxidising atmospheric conditions to pH up to 9-10 will involve the precipitation of large quantities of amorphous or poorly crystalline ferrihydrite having particle size and surface characteristics which lead to high sludge volumes and consequently to facile blocking of separation columns.
Methods of simple precipitation by raising the pH
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GEO2 Limited
Hruskoci Peter A.
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