Abstract: A low-temperature vacuum method has been developed for separation of iodine (I₂) from kelp,which involves cooking dry kelps in Na₂CO₃ aqueous solution,acidifying and oxidizing the filtrate,extraction of I₂ with organic solvents having low-boiling points,and final isolation of I₂ from the solvent at low temperature and reduced pressure.Formation of I₂ in the acidified solution was controlled by potentiometric titration using H₂O₂ aqueous solution as the oxidant.Yield of I₂ was relatively high (62.5%) which can be quantified by delta algorithm.Influences of separation conditions including pH of the filtrate,concentration of H₂O₂,and organic solvents on experiment result were comparatively investigated.Purity of I₂ acquired by this method was respectively determined by iodimetry and spectrophotometry.Results showed that it′s suitable for separation of I₂ in the pH range of 2.5~3.5 using 2% (mass fraction) H₂O₂ as the oxidant.In comparison with that of CH2Cl2,the extraction efficiency of anhydrous (CH₃CH₂)₂O was relatively higher for isolation of I₂ in aqueous solution.Data of iodimetry and spectrophotometry agreed well so that the both methods were feasible for quantifying I₂ content in aqueous solution.

Key words: lodine, H₂O₂, potentiometric titration, iodimetry, kelp