Catalytic chelation technique for the removal of toxic and heavy metals from green mussel, perna viridis

Abstract

Malaysian mussels can be contaminated with toxic and heavy metals which are cumulative poison through long term ingestion. Currently, no commercially viable technology has been developed for the removal of these toxic and heavy metals from contaminated mussels. Therefore, the purpose of the study is to develop method that safely removes metals from contaminated mussels so as to comply with the permissible limit set by the Malaysian Food Regulations (1985) and Commission Regulation of EU (2006) for human consumption. The removal of toxic and heavy metals in mussels by catalytic chelation method was studied using three types of chelating agent salts, namely trisodium citrate, disodium oxalate and sodium acetate. Three types of catalysts supported on Al2O3, namely MgO, BaO and CaO were used. The preliminary treatment conditions was carried out using trisodium citrate at a concentration of 500 mg/L, one hour treatment time, treatment temperature of 32.5±0.5oC and pH 7-8. All metals analysis were carried out using inductively coupled plasma mass spectrometry technique. The study shows that female mussel accumulates higher concentration of toxic and heavy metals as compared to male mussel. The results indicated that sodium acetate gave the highest percentage removal of toxic and heavy metals (As 59.50%, Pb 88.57%, Cd 68.01% and Ni 79.67%) followed by disodium oxalate (As 46.89%, Pb 85.46%, Cd 60.41% and Ni 47.80%) and trisodium citrate (As 38.13%, Pb 68.90%, Cd 70.49% and Ni 36.92%). Thus, all treatment conditions were optimized according to sodium acetate in subsequent study. The presence of catalysts improved toxic and heavy metals removal in mussels. Among the three catalysts studied, CaO catalyst gave the highest percentage removal (As 46.89%, Pb 85.46%, Cd 60.41% and Ni 47.80%) followed by BaO and MgO at an optimum calcination temperature of 1000oC. XRD analysis revealed the active sites were due to the presence of orthorhombic Al2O3, monoclinic CaAl4O7/CaO.2Al2O3 and cubic Ca12Al14O33 species. Meanwhile, FESEM analysis displayed the formation of homogeneous particles with undefined shape, aggregated and agglomerated on the catalyst surface. BET surface area study gave a surface area of 33.22 m2/g. EDX analysis showed a weight percentage of O=57.43%; Al=35.93%; Ca=6.64%. FTIR analysis showed total removal of metal precursor by CaO/Al2O3 catalyst at 1000oC calcinations temperature.