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THE USE OF A GLAUCONITIC CLAY TO REMOVE METALS FROM SOLUTION

Dr P R J Smith, Aquatonics Ltd, Glenthorne, Searle Street, Crediton, Devon, EX17 2DB, UK. e-mail phil@aquatonics.com

SUMMARY

A Department of Trade and Industry (DTI) SMART award is being used to fund an 18 month study of the use of a dredged spoil from Southampton Water (UK) to remove metals from effluents and polluted streams.

The results presented here are for the first 6 months of the project, and relate to the characteristics of the glauconitic sediment and its ability to remove metals from test solutions using batch processing.

The effectiveness of the glauconitic clay increased as pH approached neutral, and increased with the quantity of clay present in relation to a standard solution of metals.

At a pH of 7.0 a 2.5% slurry of glauconitic clay (dry weight) removed 99 % of copper and 90% of zinc and cadmium from a 50 ppm solution. These results compare very favourably with previous laboratory tests using glauconite to remove metals from acidic solutions, where far higher concentrations of sediment were used and copper removal was 96%, zinc 90% and cadmium 95% (Spoljaric and Crawford, 1978).

When the pH and starting concentrations of metals was kept at 50 ppm, but the concentration of glauconitic sediment was reduced to 0.5% slurry (dry weight) the copper removal was still high (95%) but removal of zinc fell to 26% and removal of cadmium fell to 29%.

The effect of pH was tested at a slurry concentration of 0.5% (dry weight). The removal of each metal was almost unchanged over the pH range 5.1 to 6.5 (copper 58 - 65%; zinc 20 - 21%; cadmium 25 - 26%) but increased strongly at a pH of 7.0 (copper 95%, zinc 31% and cadmium 38%).

At the lowest dosing rate (0.09% dry weight) of the glauconitic clay the concentration of metals in the clay after exposure to 50 ppm of cadmium, copper and zinc was very high (cadmium 1.24%, copper 8.31% and zinc 2.43%). These concentrations may be high enough to allow smelting of the metals from the clay.

Perhaps most importantly, toxicity tests showed that 0.5% glauconite had a dramatic effect on the toxicity of an actual mine water discharge, using one of the most sensitive species of invertebrate (a snail called Physa acuta). The glauconitic sediment produced a reduction in toxicity that was equivalent to a 100 fold dilution with clean water. This indicates that glauconitic clays may have a genuine role in cleaning up polluted streams and rivers, both in the UK and overseas.

e-mail phil@aquatonics.com and request a copy of the full report.

NEW BENEFICIAL USE FOR DREDGED AND LOW VALUE CLAYS

A new beneficial use of dredged clays and other low value clays has been identified by Aquatonics Ltd, who are using clays to remove metals such as copper, zinc and cadmium. Clays are used in either a slurry form or as a solid bed of clay. Results of the studies have been very encouraging, with over 95-99 % removal of copper from test solutions at a clay slurry concentration of only 0.5%. If the slurry concentration is increased to 5% then over 95% of cadmium and zinc can also be removed.

The R&D was funded by a SMART award for £45,000 from the Department of Trade and Industry. This funding allowed Aquatonics to prove the concept of using clay slurries to remove metals. The next stage will be to find Joint Venture partners to produce treatment plant that can be used at mines, manufacturers of Printed Circuit Boards (which produce a copper-rich effluent) smelting works and other industries that have metals in their effluents.

"The international market for clay slurry technology could be several hundred million dollars per year. Combined with other technologies clay slurries and clay beds have the capacity to clean up many metal-rich effluents so that they can be discharged to sewage treatment works and rivers. We have carried out the first trials of a prototype at an abandoned mine in Cornwall, and shown that clay slurries have considerable potential" said Dr Phil Smith, Director of Aquatonics.

The next stage of the research was to compare the effectiveness of clays from different sites around the world (Belize, Namibia, California and the UK). Click to view results

"We are keen to work as closely as possible with the dredging industry and its clients to find beneficial uses of both capital and maintenance dredging. We have also looked at other clays for which there is currently no commercial market. Many of these also produced excellent results" said Dr Smith.

Dr Phil Smith, Aquatonics Ltd, Glenthorne, Searle Street, Crediton, Devon, EX17 2DB, UK. Email: phil@aquatonics.com

Summaries of the research findings can be found on the Aquatonics web site

Prepared by Phil Smith, 12 May 2003