Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Organic
Reexamination Certificate
1999-10-05
2001-06-26
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Organic
C205S771000, C205S772000, C588S253000
Reexamination Certificate
active
06251258
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and apparatus for removing toxic substances from waste marine products, and more particularly to a method and apparatus for removing toxic substances from waste marine products, which extracts the toxic substances such as heavy metal and arsenic included in the waste marine products such as cuttlefishes, shellfishes, shells (scallops in particular) and fishes into an acid solution and separates/collects the toxic substances.
2. Description of Related Art
Sometimes, the toxic substances such as heavy metal (e.g., silver, copper, cadmium and zinc), arsenic and phosphorus are concentrated in the internal organs, liver and kidney of fishes and cuttlefishes and the internal organs of shells. The concentration of the heavy metal in the marine products varies according to the kinds and organs of the marine products, the seasons and the habitats. The concentration of the heavy metal is high from the summer to the autumn when the temperature is high, and the heavy metal of 30-100 mg/dried solid 1 kg or more is included in the marine products. When the temperature is low, the heavy metal of several ten mg may be included in the marine products. Arsenic of several ten mg may also be included in some kinds and organs of the marine products.
Waste marine products including the toxic substances such as heavy metal and arsenic are buried in the ground, thrown into the sea and incinerated. If a large amount of waste marine products is discarded, they become toxic wastes that may pollute the environment. It is therefore preferable to discard the waste marine products after the toxic substances such as heavy metal and arsenic are removed from the waste marine products in order to prevent the pollution of the environment.
Since the waste marine products includes protein of high concentration, the waste marine products may be reused for animal food if the concentration of the heavy metal per 1 kg of dried solid is 5 mg or less and the concentration of arsenic per 1 kg of dried solid is 1 mg or less. The concentration of heavy metal and arsenic are allowed to be higher than feed if the waste marine products are reused for fertilizers.
Accordingly, Japanese Patent Provisional Publication Nos. 8-99001 and 9-47257 disclose the technique of extracting the heavy metal included in the waste marine products into a sulfuric acid solution, or the like and electrolytically removing the heavy metal included in the extracted solution. This technique has been developed around Hokkaido prefectural industrial laboratory.
In a conventional method of removing the heavy metal in the electrolysis, the heavy metal in the waste marine products is proved to be eliminated at a high removal rate of 99% or more, but the waste marine products must be processed for dozens of hours (Japanese Patent Provisional Publication No. 8-99001) and for about twenty-four hours (Japanese Patent Provisional Publication No. 9-47257) until the concentration of the heavy metal is reduced to an allowable value of 5 mg/dried solid 1 kg.
In addition, the deposit including the heavy metal is accumulated on the surfaces of the electrodes, and the protein in the waste marine products is adhered to the surfaces of the electrodes. This remarkably lowers the heavy metal deposition efficiency.
The deposition efficiency is lowered since the heavy metal, which is excessively deposited on the surfaces of the electrodes, is separated from the surfaces of the electrodes or the adhesive deposit including the heavy metal is adhered to the surfaces of the electrodes.
To address this problem, when the deposit including the heavy metal is excessively accumulated on the surfaces of the electrodes and the surfaces of electrodes become unclean, the surfaces of the electrodes are cleaned by rubbing the surfaces of the electrodes by brush, sponge, or the like to recover the deposition efficiency.
In the case of experimental equipment used in a laboratory, the surfaces of the electrodes can be rubbed by the brush and the sponge, but a large plant has dozens of electrodes with surface area of 1 m
2
or more. Thus, the weight of the plant is in the metric ton level. In the case of the large plant, it is impossible to take out the electrodes from the electrolytic bath, clean the electrodes and then mount the electrodes in the electrolytic bath if the cleaning time and labor are taken into consideration.
Arsenic and phosphorus as well as the heavy metal are extracted into the acid solution, and thus, it is necessary to separate and collect arsenic as well as the heavy metal.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide the method and apparatus for removing the toxic substances from the waste marine products, which makes it possible to remove the toxic substances such as heavy metal and arsenic from the waste marine products with extremely high efficiency at low cost.
To achieve the above-mentioned object, the present invention is directed to a method of removing a toxic substance from waste marine products, the method comprising: an extraction step of bringing waste marine products including heavy metal as a toxic substance into contact with an acid solution including at least one of sulfuric acid and hydrochloric acid to thereby extract the heavy metal from the waste marine products into the acid solution; an electrolysis step of applying a direct current voltage between electrodes provided in the acid solution, into which the heavy metal is extracted, to thereby deposit the heavy metal in the acid solution on the electrodes; and an electrode cleaning step of reversing the polarity applied between the electrodes in a neutral or alkali electrolytic solution from the polarity in the electrolysis to thereby remove the heavy metal from the electrodes.
According to the present invention, the heavy metal included in the waste marine products is extracted into the acid solution including at least one of sulfuric acid and hydrochloric acid, and the direct current voltage is applied between the electrodes provided in the acid solution to deposit the heavy metal in the acid solution on the electrodes. If the heavy metal, or the like excessively deposits on the electrodes to lower the deposition efficiency, the polarity of the electrode applied between the electrodes in the neutral or alkali electrolytic solution is reversed from the polarity in the electrolytic deposition to thereby remove the heavy metal from the electrodes. This enables the efficient removal of the heavy metal from the waste marine products and drastically reduces the electrode cleaning time.
According to the present invention, the acid solution in slurry, which is formed by mixing powder of the waste marine products and the acid solution, is circulated between the extraction step and the electrolysis step to extract the heavy metal and deposit the heavy metal on the electrodes. This improves the extraction efficiency and the deposition efficiency of the electrodes.
According to the present invention, the circulating flow of the acid solution circulated between the extraction step and the electrolysis step is formed by a rising force of bubbles in the air blown into the acid solution, the bubbles rising between the electrodes. This makes the circulation slower than the circulation by the mechanical force of a stirrer, or the like, so that the heavy metal can be separated from the electrodes by force of the circulating flow.
According to the present invention, if the waste marine products includes arsenic as a toxic substance, an alkali agent and a flocculant are added to the acid solution, from which the waste marine products is separated after the electrolysis step, to thereby adjust the acid solution to pH8-11.5 so that flocculation including arsenic can sediment in the acid solution. This enables the removal of arsenic, which is extracted at the extraction step but is hardly removed at the electrolysis step.
According to the present invention, i
Asakura Hiroshi
Hishinuma Toshiyuki
Ichikawa Hiroyuki
Kasai Masataka
Kojima Masayuki
Hitachi Plant Engineering & Construction Co. Ltd.
Oliff & Berridg,e PLC
Phasge Arun S,.
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