본문 바로가기
HOME> 논문 > 논문 검색상세

논문 상세정보

Water research v.30 no.5, 1996년, pp.1149 - 1160  

Mécanisme de la précipitation de l'acide salicylique par coagulation par le fer ferrique
Mechanism of salicylic acid precipitation by Fe(III) coagulation

Rahni, Mohamed ; Legube, Bernard ;
  • 초록  

    Abstract The general objective of our work is to study the precipitation mechanism of organic matter by iron salts. The elimination of aromatic acids by coagulation with iron was found to depend on the number and the position of acid functions on the aromatic cycle. Only compounds which present at least two COOH and/or OH functions in ortho position were significantly removed by iron(III) coagulation (Lefebvre and Legube, 1993). The objective of the present paper is to precise the mechanisms of interaction between salicylic acid (and its isomers) and iron as well as to evaluate the part of complexation reactions. All experiments were carried out with a jar-test apparatus which was described in a previous publication (Lefebvre and Legube, 1990). The coagulation was carried out at 250 r.p.m. for 15 min, the slow agitation (floculation) was carried out at 30 r.p.m. for 30 min, 2 h were chosen for the sedimentation. After filtration on 0.2 μm-membrane, the following analyses were performed: dissolved organic carbon (DOC), analysis of aromatic compounds by HPLC, measurement of u.v.-visible absorbance, analysis of iron by orthophenanthroline-spectrophotometric method (dissolved iron) and by atomic absorption spectrometry (total iron). The main results presented in this paper are: 1. (i) The removal of salicylic acid by coagulation with iron was optimal for pH values of about 5.5 [Fig. 1(B)] where this removal increased with the increasing coagulant dose [Fig. 1(A)]. Furthermore, at pH 3.5 (Table 1), one could notice appearance of an absorbance band at 525 nm and a significant difference between results of DOC and HPLC analyses for weak molar ratios. At pH 5.5 (Table 2), the difference between both determination technics of salicylic acid (DOC and HPLC) was significant only for a salicylic acid/iron molar ratio above 0.8. This difference between the two analytical methods was mainly observed with the samples containing residual iron and which presented a 483 nm-band on the visible spectra. At pH 8.5 (Table 3) the precipitation of iron was predominant, which can explain the weak removal of the compound. 2. (ii) The relative position of hydroxyl and carboxyl functions on the aromatic ring of hydroxy-benzoic acid was found to be very important. Indeed, the removal of 3-hydroxybenzoic (meta position) and 4-hydroxybenzoic (para position) acids were found to be much lower than salicylic acid. Moreover, the organic matter/iron molar ratio for coagulation, at pH 5.5, of the two salicylic acid isomers had no effect either on the elimination of the compounds nor on the solubility of iron (Tables 5 and 6). We conclude from these results and some others (stoichiometry of the complex formation in Fig. 7, effect of pH on the complex stability in Fig. 8) that precipitation of salicylic acid by coagulation with iron is firstly the consequence of the initial formation of a soluble complex with a 1/1 stoichiometry. The formation of this soluble complex was particularly easy to observe at acidic pH and for high salicylic acid/iron molar ratios. The complex stability is due to the bidentate nature of the salicylate ligand, considering the fact that there was evidently no formation of such a complex from meta and para isomers of salicylic acid and only a weak precipitation of these compounds was observed. Secondly, increase of pH leads to hydrolysis of the complex by the partial replacement of salicylic acid with hydroxide ions. During the hydrolysis, the maximum of the absorption band of spectra was found to shift (483 nm at pH 5.5 instead of 525 nm at pH 3.5), then to disappear when pH values are nearly neutral. This hydrolysis leads only to a partial precipitation of the organic compounds, even for optimal pH values (around 5.5).


    Résumé L'étude de la coagulation-floculation des acides 2-hydroxy, 3-hydroxy et 4-hydroxy benzoïques par le chlorure ferrique à différents pH et à différents rapports molaires (matière organique/fer), a montré que la zone optimale d'élimination de ces composés correspond aux valeurs de pH situées autour de 5,5 et à des faibles rapports molaires (composé organique/fer). L'acide salicylique est mieux éliminé que ses deux isomères, sa précipitation est la conséquence de la formation initiale d'un complexe 11. Ce complexe est stable en raison de la nature bidentate du ligand salicylate, compte tenu de sa non formation apparente avec les isomères méta et para. L'augmentation du pH, entraîne une hydrolyse partielle du complexe par remplacement de l'acide salicylique par des ions hydroxydes. Cette hydrolyse conduit à une précipitation importante, mais toutefois incomplète, du composé organique.


  • 주제어

    coagulation-floculation .   fer ferrique .   acide salicylique .   ligand bidentate .   complexe .   mécanisme .   coagulation-floculation .   iron(III) .   salicylic acid .   bidentate ligand .   complex .   mechanism.  

 활용도 분석

  • 상세보기

    amChart 영역
  • 원문보기

    amChart 영역

원문보기

무료다운로드
  • 원문이 없습니다.

유료 다운로드의 경우 해당 사이트의 정책에 따라 신규 회원가입, 로그인, 유료 구매 등이 필요할 수 있습니다. 해당 사이트에서 발생하는 귀하의 모든 정보활동은 NDSL의 서비스 정책과 무관합니다.

원문복사신청을 하시면, 일부 해외 인쇄학술지의 경우 외국학술지지원센터(FRIC)에서
무료 원문복사 서비스를 제공합니다.

NDSL에서는 해당 원문을 복사서비스하고 있습니다. 위의 원문복사신청 또는 장바구니 담기를 통하여 원문복사서비스 이용이 가능합니다.

이 논문과 함께 출판된 논문 + 더보기