Collector for adsorptive recovery of dissolved metal from sea water

US Patènt # 6863812

Invèntors:	Sugo; Takanobu (Gunma-ken, JP); Katakai; Akio (Gunma-ken, JP); Seko; Noriaki (Gunma-ken, JP)
Assignee:	Japan Atomic Energy Research Institute (Tokyo, JP)
Appl. No.:	427942
Filed:	May 2, 2003

SUMMARY OF THE INVÈNTION

(a) The present has been accomplished with a view to developing a material that is strong enough to withstand hostile weather conditions in ocean and which has high performance in collecting dissolved metals from seawater. To attain this object, the fiber of a polyolefin such as polyethylene or polypropylene that is a highly durable polymer is used as a substrate, side chains are grafted to the substrate polymer by radiation-initiated graft polymerization, and then an amidoxime group and a hydrophilic group are introduced into the same graft side chains.

The collector of the invèntion is produced by a process comprising the following steps: (1) to generate a reaction initiating species (radicals), a substrate comprising the fiber of a polyolefin such as polyethylene or polypropylene is exposed to electrons; (2) grafting a polymerizable monomer having a cyano group such as acrylonitrile (CH.sub.2.dbd.CHCN) onto the polyolefin fiber in the presence of a polymerizable monomer having a hydrophilic group; and (3) then reacting the cyano groups in the graft side chains with hydroxylamine (NH.sub.2 OH) to convert them to amidoxime groups, whereby both amidoxime and hydrophilic groups are introduced into the same graft side chains.

If desired, grafting of the polymerizable monomer having a cyano group onto the polyolefin fiber in the presence of the polymerizable monomer having a hydrophilic group is performed at a properly adjusted molar ratio of the two polymerizable monomers and, thereafter, the cyano groups in the graft side chains are reacted with hydroxylamine (NH.sub.2 OH) to be converted to amidoxime groups, whereby the amidoxime and hydrophilic groups are introduced at a molar ratio of 70:30-30:70, preferably 60:40-40:60, more preferably 50:50.

(b) The collector of the invèntion needs only to be submerged and anchored in seawater such as the Kuroshio current so that slightly dissolved useful metals such as vanadium, uranium, cobalt, titanium and molybdenum are efficiently recovered from the seawater. The collector is characterized in that the fiber of a polyolefin such as polyethylene that is commonly used in oil fences is irradiated to introduce a chemical structure capable of selective trapping of metals.

Specifically, the collector of the invèntion can be produced by one of the following methods: (a) acrylonitrile is grafted to a substrate fiber in the form of either a nonwoven or woven cloth of the fiber of a polyethylene such as polypropylene or polyethylene and amidoxime groups are introduced into the graft side chains; (b) acrylonitrile and a polymerizable monomer having a hydrophilic group are co-grafted to the substrate fiber in either nonwoven or woven cloth form and amidoxime groups are introduced into the graft side chains made of acrylonitrile; and (c) the fiber of a polyolefin such as polypropylene is coated with a different polyolefin such as polyethylene to form a fiber of a core/sheath structure, a substrate is formed of this fiber in the form of either a nonwoven or woven cloth, either acrylonitrile or a polymerizable monomer having a hydrophilic group or both are grafted to the substrate fiber, and amidoxime groups are introduced into the graft side chains made of acrylonitrile.

For actual use, a plurality of such collectors are superposed and sandwiched between nets and a plurality of the resulting assemblies are stacked in position at suitable spacings to construct a cassette of collectors.

To collect dissolved metals from seawater, the cassette is placed in a number of corrosion-resistant cages, which are bound to a rope at suitable spacings; an anchor is attached to the submerged end of the rope and a buoy is attached to the other end so that the cassette is anchored in seawater either depthwise or laterally as long as the collectors are kept in contact with the seawater to collect dissolved metals from it.

BRIEF DESCRIPTION OF THE DRAWINGS

FÌG. 1 is a graph showing the ratio of grafting onto a nonwoven cloth as a function of time in accordance with the invèntion;

FÌG. 2 is a graph showing the relationship between the reaction time for conversion to amidoxime groups and the rate of uranium trapping in accordance with the invèntion;

FÌG. 3 shows the functional groups generated in the reaction for conversion to amidoxime groups;

FÌG. 4 shows two types of functional group distribution in the fractured surfaces of fibers produced by graft polymerization in the invèntion;

FÌG. 5 is a graph comparing three methods of graft polymerization in terms of the rate of uranium trapping;

FÌG. 6 shows three different cross-sectional shapes for the fiber used in the collector of the invèntion;

FÌG. 7 is a graph showing how the rate of uranium trapping by the collector of the invèntion varies with its specific surface area;

FÌG. 8 is a graph showing the durability of the collector of the invèntion;

FÌG. 9 illustrates how the collector of the invèntion is anchored in seawater to collect dissolved metals;

FÌG. 10 is a graph showing how the results of uranium trapping by the collector of the invèntion vary with the method of graft polymerization;

FÌG. 11 is a graph showing how the adsorbing performance of the collector of the invèntion is affected by the depth to which it is submerged in seawater;

FÌG. 12 is a graph showing the performance of the collector of the invèntion in trapping vanadium and uranium;

FÌG. 13 illustrates the structure of the collector cassette of the invèntion; and

FÌG. 14 shows two different distributions of uranium adsorption as observed in the collector cassette of the invèntion.