Patent ID: 10724118

Abstract:
The invention refers to a method for recovering copper from waste fishing nets. The method of the invention includes washing of nets in a washing liquid, wherein an antifouling coating and other impurities are removed from the surface of the nets to a largest extent possible. The washing liquid is water; NaOH can also be added into the water in order to improve the efficiency of washing, such that the NaOH concentration in the water is up to 20%. The suspension of the washing liquid, sludge and other impurities, resulting from the washing step, is led to a separation step. The sludge obtained in the separation step is led to the dissolution step in an acidic medium. A strong mineral acid is selected as the acidic medium, such as H2SO4, HNO3, HCl, a mixture of strong mineral acids or a mixture of one or several strong mineral acids with H2O2. Then, the non-dissolved sludge is separated from the solution of copper ions Cu2+ in the acidic medium, the solution of copper ions Cu2+ in the acidic medium is led to electrolysis, wherein elementary copper having a purity of more than 94% is deposited on the cathode. The non-dissolved residual sludge can be optionally led to thermal treatment to the reactor, where the residual paraffins and co-polymers are removed at a temperature ranging from 500° C. to 900° C. The remaining ash may contain up to 30% by weight of copper compounds based on the weight of the ash, particularly in the form of copper(ll) oxide CuO, less in the form of copper(l) oxide Cu2O and copper phosphates Cu(H2PO4)2, Na6Cu9(PO4)8. This ash is then led to dissolution in the acidic medium and to further steps of the method. The proposed method of the invention improves the method for recycling waste nets, such that not only pure polyamide is obtained from the nets but also elementary copper, which has a double benefit: elementary copper in a sufficiently pure form is a useful raw material, moreover, the quantity of copper in final waste is reduced, consequently a negative impact on the environment is reduced and the cost of waste disposal of the method is reduced as well.