Engineering & Mining Journal

JUN 2016

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JUNE 2016 • E&MJ; 83 www.e-mj.com OPERATING STRATEGIES the lake during the phases of full circu- lation in spring or autumn. Distribution of the lime suspension is therefore entirely natural and does not require any external energy source. In this manner, the pH val- ue was increased from 2.9 to 7. "The neutral range is between approx- imately six and eight," Strzodka contin- ued. "Water circulation was used once more in a secondary treatment from May to August 2014, which had become nec- essary due to reacidifi cation of the lake caused by infl owing water with an acidic pH value—3,000 mt of lime products in a 400,000-m 3 suspension was introduced during this period, creating an alkali buf- fer of 0.18 mol/m 3 ." In June 2015, the plant was updat- ed for a second stage, which involved the introduction of CO 2 to the lake to induce hydrocarbonation. Here, the suspended CO 2 was fed into the hypolimnion, or low- er layer, via the lake bed while the forced infl ow of lime remained directly beneath the surface of the water. The process ini- tially utilized the lake's layering phase that occurs in summer and winter to add the two suspensions to the water in sepa- rate layers. In the subsequent full-circu- lation phase, an entirely natural blending took place, thus allowing the lime to react with the CO 2 . "We would have needed a massive facility to produce hydrocarbonation out- side the lake. Maintenance and operation alone would have been extremely costly. In contrast, our new method of using full circulation of the lake is practically free and very effi cient. The lake itself is used as a fully equipped reaction chamber," said Strzodka. With the simultaneous treatment of the lake with lime and CO 2 , a buffer is created and the water body requires far less additional treatment, leading to signifi cantly lower costs. The treatment is complete as soon as the bi- ological processes themselves restore the natural balance to the lake. Scholz said, "The GSD system proved extremely effective during initial neu- tralization of Lake Scheibe and is there- fore outstanding value for money. Also, the project management team at GMB GmbH, the scientifi c advisers and the system engineers always managed to promptly fi nd remedies to technical is- sues that arose during the operational phase." The method is particularly suit- able for expansive lakes with signifi cant acid infl ow, as large volumes can be treat- ed in a short period. In addition to building another UNP system at Lake Bernstein, GMB GmbH is already looking for additional applica- tions. "As things stand, the system con- fi guration and operation are specifi cally designed for Lake Scheibe. So we are cur- rently reviewing what standardization of the system components might look like," said Strzodka. Defi ning standard sizes for the fl oating pipes, pumps, the mixer and the nozzles would allow the method to be used to treat smaller ponds. This aerial view shows the pattern of distribution of a lime suspension from a set of nozzles fl oating just under the water's surface. The initial treatment raised the pH of the lake water from 2.9 to 7. A 4% suspension consisting of 15,200 mt of slaked lime mixed in lake water was pumped into the lake at a velocity of 7.6 m/s and a fl ow rate of 260 m 3 /h, six days per week over a period of 16 weeks.

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