New method remove heavy metals from water

New method to remove heavy metals from water

12:51 AM, 26th December 2011
New method to remove heavy metals from water
Heavy metal removal, Brown engineers have devised an automated system that combines chemical precipitation with electrolytic techniques in a cyclic fashion to remove mixtures of trace heavy metals from contaminated water.

RHODE ISLAND, US: An unfortunate consequence of many industrial and manufacturing practices is the release of heavy metals in waterways. These metals can remain for decades, in low concentrations and still be dangerous. Engineers at Brown University have developed a system that efficiently removes trace heavy metals from water. In experiments, the researchers showed that the system reduced cadmium, copper and nickel concentrations, returning contaminated water to near or below federally acceptable standards. The technique is scalable and has viable commercial applications, especially in environmental remediation and metal recovery fields.

Joseph Calo, Professor, Emeritus of Engineering and maintains an active laboratory at Brown University, and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning / precipitation (CEP) system, removes up to 99 per cent of copper, cadmium and nickel, returning the contaminated water to federally accepted standards of cleanliness.

A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte, known as electrowinning, electrolytic removal/recovery or electroextraction. The main drawback to this technique is that there must be high-enough concentration of metal cations in water for it to be effective.

The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the pH of water, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The “clear” water is siphoned off and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.

When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place and metal cations are chemically changed to stable metal solids so they can be easily removed. In experiments, the engineers tested the CEP system with cadmium, copper and nickel, individually and with water containing all three metals. The results showed cadmium, copper and nickel were lowered to near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.

© Brown University News



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