US 5,476,994 AGranted

Method for extracting metals from sediment

AssigneeGreenfield Environmental

InventorGeorge J. Trezek

Life of this patent

Estimating the term…

Loading patent…

Abstract

The process for removal of metal-contaminated sediment includes dredging the sediment and removing large objects from the sediment, then removing smaller objects such as shell fragments with a first course screen. The remaining sediment slurry is processed through at least two screens covering a range of mesh sizes to separate the solids into three size/mesh fractions. Water extracted during the separation is processed through a series of hydrocyclones to separate any remaining solids and to allow the water to be recycled. The largest fraction of solids, the "sand fraction" has a low concentration of the metal and requires no further processing. The smallest fraction, which has passed through a mesh corresponding to the size of the most basic form of the metal ore, enters a screw classifier for dewatering after which it is appropriate for direct smelter recycling. The mid-size fraction, while still containing elevated levels of the metal which make it unsuitable for land-based use, does not contain sufficient concentrations for direct smelter recycling. This fraction is passed through a chemical extraction system to create a soluble metal salt from which a precipitate is formed which is then suitable for smelting.

A process for extracting and reclaiming metallic contamination from sediment comprising the steps of:

removing large oversize articles from the sediment;
diluting the sediment with water;
passing the sediment through a first screen to remove small oversize debris;
passing the sediment through a first hydrocyclone for dewatering said sediment to produce a first overs fraction comprising removed water from the sediment and a first unders fraction;
passing the first unders fraction through a plurality of second screens for separating said first unders fraction into a sand fraction, a fine fraction, and a mid-size fraction wherein said sand fraction has a low metal concentration, said fine fraction has a high metal concentration and said mid-size fraction contains a sufficient metal concentration to make it unsuitable for return to an environment;
dewatering the fine fraction to produce a first fraction of high metal content solids, retaining the removed water from the fine fraction for further processing;
transferring the removed water from the fine fraction and the first overs fraction to at least one second hydrocyclone having a smaller diameter than that of said first hydrocyclone, said at least one second hydrocyclone generating a second overs fraction comprising clarified water for recycling and a second unders fraction;
placing the second unders fraction in a settling tank wherein a second fraction of high metal content solids are settled;
extracting clarified water from said settling tank for recycling;
transferring the mid-size fraction to a chemical reactor;
reacting the mid-size fraction with a chemical reagent within said reactor whereby said metal within the mid-size fraction is placed in a solution;
passing the solution through a third screen to extract a solids suspension;
neutralizing the chemical reagent and its byproducts in the solids suspension and the solution;
precipitating said metal in said solution into a third fraction of high metal content solids;
and
drying all fractions of high metal content solids for recycling.

13 more elements

Abstract

Claims19