Study on the Absorption of Heavy Metal Ion Pb²⁺ by the Low Methoxy Pectin from Sunflower Heads

Heavy metal pollution poses a serious threat to public health due to lacking of effective treatment methods. In order to develop new biological materials for adsorption of heavy metal ions, the natural low-methoxyl pectin (termed LAHP) was extracted from dried heads of sunflower in this study. The adsorption capacity of LAHP for Pb²⁺ in aqueous solution was studied and the conditions for the adsorptions were optimized. LAHP was extracted by oxalic acid solution at 80 ^oC and precipitated by ethanol with the yield of 14.68%±0.76%. The composition analysis showed that LAHP met the requirements of national quality standard for pectin as a food additive. The structure analysis showed that LAHP was natural low-methoxyl pectin, which was mainly composed of galacturonic acid (GalA, 86.34%) with a low degree of methyl esterification (23.93%±1.57%) and high molecular weight (257 kDa). The adsorption capacity of Pb²⁺ by LAHP was affected by the amount of pectin, pH of solution, temperature and interference ions. The optimal conditions for the adsorption of Pb²⁺ were determined as follows: pectin dosage was 30 mg/L (concentration of Pb²⁺ was 11.0 mg/L), pH of solution was 8.0, and the temperature was 30 ℃. The maximum adsorption capacity of LAHP for Pb²⁺ was 44.57±2.50 mg/g, and would be reduced to some extent affected by divalent metal ions. Therefore, the low-methoxyl pectin from sunflower heads would be a kind of natural heavy metal adsorbent, which had a wide application prospect.