Chloride is the most common interference and has the greatest effect on COD test results. I have a sample containing 10000-100000 ppm chloride (seawater). in low concentration of chloride we should use mercuric sulfate to form complex with chloride but mercury is very toxic and use it for low concentration of chloride. what do you suggest for chloride removal in this sample? ( except use of mercury or sample dilution)
thanks
Dear Bahram,
You may use Mg−Al oxide. For more on this method, please see the publication entitled "Simultaneous removal of Cl− and SO4 2− from seawater using Mg−Al oxide: kinetics and equilibrium studies " contained in the following link:
Mg−Al oxide, obtained by the thermal decomposition of a CO3 2−-intercalated Mg−Al layered double hydroxide (CO3·Mg−Al LDH), simultaneously absorbed Cl− and SO4 2− from seawater and generated a Mg−Al LDH intercalated with Cl− and SO4 2−. The Mg−Al oxide with a molar ratio Mg/Al = 4 was more superior than the oxide with Mg/Al = 2 for Cl− removal, whereas a reverse phenomenon was observed for SO4 2− removal. The removal of Cl− and SO4 2− by the Mg−Al oxide with Mg/Al = 4 could be represented by first-order and pseudo second-order reactions, respectively. The removal of both Cl− and SO4 2− by the Mg−Al oxide with Mg/Al = 2 could be represented by a pseudo second-order reaction. The removal of both Cl− and SO4 2− by the Mg−Al oxides with Mg/Al = 4 and 2 was proceeded under chemical reaction control. The adsorption isotherms for Cl− and SO4 2− adsorbed by the Mg−Al oxides could be expressed by Langmuir-type adsorption. These reactions were derived from monolayer adsorption, indicating the intercalation of Cl− and SO4 2− in the interlayer space of Mg−Al LDH. The uptake of Cl− and SO4 2− from seawater by Mg−Al oxide was proceeded spontaneously.
http://link.springer.com/article/10.1007/s13201-014-0224-4
Hoping this will be helpful,
Rafik
Thanks dear rafik
Fig.1 show chloride removal versus time in this article. It's clear the maximum extent of chloride removal is 67% in 60 'C and less than 25 % in 10'C. Then if we use a sample with 100000ppm chloride, results show us 67000ppm chloride removal in optimum condition reaction and 33000ppm chloride concentration is over range for Chemical oxidation demand test. less than 1500ppm is good for COD test. But it's a good idea for low concentration chloride. I should keep studying more
Thanks again my dear friend
Hi dear Min Gao
you can precipitate chloride ion by silver nitrate as silver chloride then separate it but AgNO3 has another interference (NO3) for COD Test. so we should do a pretreatment or choose a good precipitant agent.
HI Stefanos Giannakis
I checked it and according this manual COD vial contains mercuric sulfate will eliminate chloride interference up to 15000ppm in HIGH RANGE PLUS and we should dilute samples to reduce chloride concentration to the given level. but when COD is for example 500ppm and chloride is 100000ppm we couldn't dilute it very much because we lost COD ppm.
In one of the articles they suggest a resin for chloride removal. they called it (styrene base cation exchange ion in silver) . but i don know what is this and how can i find it?
I Think it has a selectivity for chloride removal but there is no explanation about it in this article
Puedes intentar realizar una evaporación del material a baja temperatura para así precipitar la mayor cantidad de cloruro de sodio sin que la materia orgánica presente se afecte en su contenido, de esta forma la concentración de iones de cloruro disminuye
Hi dear Kleveer Espino
Excuse me because I do not understand Spanish.I would be grateful if you write in English
Tries To realize an Evaporation of the material of a low Temperature paragraph Like that to precipitate the Major Quantity of chloride of sinned sodium That the organic matter falls ill Present in contents, of this forms the Concentration of Ions of chloride Diminishes
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