Improvements in and relating to the recovery of complexing agents from spent solutions

摘要

Aminocarboxylic acid type chelating agents of the formula FORM:0824275/III/1 wherein X is H, -CH2CH2OH, -CH2COOM, -CH2CH2COOM (M being an alkali metal, such as Li, Na or K, or ammonium base), or FORM:0824275/III/2 (in which "Alkylene" is a C2-6 group placing C2-3 between the nitrogens, such as ethylene, propylene, isopropylene or cyclohexylene, and n is 0, 1, 2, 3, 4 or more), A and B are independently H, -CH2CH2OH, -CH2COOM or -CH2CH2COOM, provided at least one of A, B or X is -CH2COOM, or -CH2CH2COOM, are recovered from aqueous solutions of their complex metal chelates with metals such as Ca, Mg, Pb, Cu, Ni, Co and Fe by adjusting the pH of said solution to a level of 6 or greater favourable to the precipitation of a particular insoluble compound of the chelated metal, adding to said medium an anion which forms said insoluble compound with the chelated metal at the adjusted pH of the solution thereby to precipitate said metal as said compound, separating the precipitate from the medium and recovering the said medium containing the chelating agent. The metals may be precipitated as sulphides or hydroxides, which may subsequently be recovered. The process may be used in conjunction with the use of chelating agents of the above formula to remove boiler and evaporator surface scale, the recovered chelating agent being recycled to the scale treatment step. Specified chelating agents are glycine, nitrilotriacetic acid, ethylenediamine tetra-acetic acid, monoethanol-ethylenediamine triacetic acid and diethanol-ethylenediamine diacetic acid.ALSO:Aminocarboxylic acid type chelating agents of the formula FORM:0824275/IV (b)/1 wherein X is H, -CH2CH2OH, -CH2COOM, -CH2CH2COOM (M being an alkali metal, such as Li, Na or K, or ammonium base), or FORM:0824275/IV (b)/2 (in which "Alkylene" is a C2-6 group placing C2-3 between the nitrogens, such as ethylene, propylene, isopropylene or cyclohexylene, and n is 0, 1, 2, 3, 4 or more), A and B are independently H, -CH2CH2OH, -CH2COOM or -CH2CH2COOM, provided at least one of A, B or X is -CH2COOM, or -CH2CH2COOM, are recovered from aqueous solutions of their complex metal chelates with metals such as Ca, Mg, Pb, Cu, Ni, Co and Fe by adjusting the pH of said solution to a level of 6 or greater favourable to the precipitation of a particular insoluble compound of the chelated metal, adding to said medium an anion which forms said insoluble compound with the chelated metal at the adjusted pH of the solution thereby to precipitate said metal as said compound, separating the precipitate from the medium and recovering the said medium containing the chelating agent. The metals may be precipitated as sulphides or hydroxides, which may subsequently be recovered. The process may be used in conjunction with the use of chelating agents of the above formula to remove boiler and evaporator surface scale, the recovered chelating agent being recycled to the scale treatment step. Specified chelating agents are glycine, nitrilotriacetic acid, ethylenediamine tetra-acetic acid, monoethanol-ethylenediamine triacetic acid and diethanol-ethylenediamine diacetic acid.ALSO:Aminocarboxylic acid type chelating agents of the formula: FORM:0824275/II/1 wherein X is H, -CH2CH2OH, -CH2COOM, -CH2CH2COOM (M being an alkali metal, such as Li, Na of K, or ammonium base), or -(Alkylene - NH) n - Alkylene - FORM:0824275/II/2 (in which "Alkylene" is a C2-6 group placing C2-3 between the nitrogens, such as ethylene, and n is 0, 1, 2, 3, 4 or more), A and B are independently H, -CH2CH2OH, -CH2COOM or -CH2CH2COOM provided at least one of A, B or X is -CH2COOM, or -CH2CH2COOM, are recovered from aqueous solutions of their complex metal chelates with metals such as Ca, Mg, Pb, Cu, Ni, Co and Fe by adjusting the pH of said solution to a level of 6 or greater favourable to the precipitation of a particular insoluble compound of the chelated metal, adding to said medium an anion which forms said insoluble compound with the chelated metal at the adjusted pH of the solution thereby to precipitate said metal as said compound, separating the precipitate from the medium and recovering the said medium containing the chelating agent. The metals may be precipitated as sulphides or hydroxides, which may subsequently be recovered. The process may be used in conjunction with the use of chelating agents of the above formula to remove boiler and evaporator surface scale, the recovered chelating agent being recycled to the scale treatment step. Specified chelating agents are glycerine nitrilotriacetic acid, ethylenediamine tetra-acetic acid, monoethanol-ethylenediamine triacetic acid and diethanol-ethylenediamine diacetic acid.