ABSTRACT. Chromium is used for plating and in chrome steel. The chromates [chromium (VI)] have many industrial uses as pigments, catalysts, fungicides. The waste waters with chromate are usually presented in industries side by oxalic acid produced at aluminum protection surface. This paper proposed a very cheep method for reciprocally treatment due to function as a bidentate ligand of oxalic acid in the form of dianion with many transition metals ions. Preparation of oxalate chromate potassium salt was made in form of K[sub]3[/sub][Cr(C[sub]2[/sub]O[sub]4[/sub])[sub]3[/sub]] anhydrous, using a suitable ratio from oxalic acid, potassium chromate and sulfuric acid. The crystals have been deposited, filtered and washed with ethanol. The product is dried and the yield calculated as a percentage based on chromium is dried.
Keywords: chromate, waste waters, oxalic acid
(ProQuest: ... denotes formula omitted.)
INTRODUCTION
There are a lot of dates and experimental research about treatment of waste waters containing Cr(VI) which can appears from different sources in a various concentration as diluted solutions or concentrated fluids.
The most investigated sources are electroplating works, tanneries, pigments, where chromate anion concentration begins with 5-50 ppm and may be attends 200-1000 ppm1-3.
The treatment of waste waters with chromium hexavalent shape content are made by chemical reduction method, using reactive agents like FeSO4, Na2SO3 NaHSO3, Na2S2O5, SO2 gaseous, (Fe + H2SO4) or electrochemically. All the reduction reactions had taken place in acid range, pH 2-2,5 in the presence of sulfuric acid usually.
By electrochemical reducing it is known a suitable method involving coagulation process assured by Fe(OH)3.
If besides of chromate anions there are an eloxal process (on alluminium) with oxalic acid, then appears also waste waters with oxalic acid.1 The high concentration of oxalate anion in the presence of sulfuric acid might be a good notification for reciprocally treatment waste waters coming from chromium electroplating and waste waters coming from aluminum protect surface by eloxal process.
* hexavalent chromium could be reduced by oxalic acid in the presence of sulfuric acid
* it could be obtained a new trivalent chromium compound in the shape of oxalate/chromium complex
MATERIALS AND METHODS
All the reagent were chemically pure or ultra pure: Merck, Fluka, Reanal in the next order: potassium chromate 0,1M sulfuric acid 1:2 vol, potassium permanganate 0,1N (F=1), oxalic acid 0,5M (F=1), Mohr salt 0,1N (F=1), sodium hydroxide 0,1N (F=1), standard chromium etalon 0,05 mg/mL, deionised water.
The apparatus were: analytical balance Tolledo, spectrophotometer UV-VIS, IR-Spectrophotometer KBr cell, magnetic stirrer. The hexavalent chromium content was tittrimetrical determined with Mohr salt 0,1N and potassium permanganate 0,1N in sulfuric acid range., pH 2. Oxalate anion was analysed titrimetrically with potassium permanganate on boiling4. The traces of hexavalent chromium untransformed in chromium oxalate complex compound was photometrical determined by means of diphenylcarbazide at 573 nm, together with Cr(III), between 1 and 20 mg/l. The cation Cr(III) was eliminated by precipitation with sodium hydroxide at 600C and pH 95. In the filtrate was determined Cr(VI). The chemical equation to obtain oxalate chromium potassium salt compound is:
...
It was prepared one saturated potassium chromate solution acidified with sulfuric acid at 70-800C, under magnetic stirrer, was added a little quantities from 0,5M oxalic acid as long as solution has a violet color.
After chemical reaction, a violet crystals of K[sub]3[/sub][Cr(C[sub]2[/sub]O[sub]4[/sub])[sub]6[/sub]] have been separated.
STUDY AREA
The influence of the oxalic acid concentration upon extraction degree of a K[sub]3[/sub][Cr(C[sub]2[/sub]O[sub]4[/sub])[sub]6[/sub]] was studied in accordance with Table 1.
RESULTS AND DISCUSSIONS
The results presented in Table 2, allowed to calculate the formula conversion percentage from Cr(VI) to Cr(III), as follows:
...(2)
...(3)
where:
Ni = initial mol number of chromium (VI),: 210-3
Nf = final mol number of chromium (VI)
The residual hexavalent untransformed chromium was calculated from Table 2 and formula (3) :
The excess of oxalic acid increase the extraction degree up to 99,80% being a good factor for process efficiency and a cheep complexation reagent.
The chromium oxalate complex was determined by IR spectrophotometer (Germany) and its diagram shows in figure 1 (see below).
The IR-spectrum analysis is representative for oxalate anion between wave numbers of our compound. The vibration from 900 cm-1 corresponds to C-C bond. The signals between 1650-1200 cm-1 attribute to vibration band from C=O and C-O bonds. The last vibration band is very large and dues by O-H bond. In spectrum can see deformation bands, äH-O-H between 1700-1640 cm-1 and äO-H from 1450 to 1210 cm-1.
CONCLUSIONS
The reciprocal treatment of hexavalent chromium and oxalic acid presented in waste waters coming for electroplating surfaces works, might be successfully applied as well as, the both concentration are large.
The optimal excess of oxalic acid are 100%.
The maximum extraction degree was 99% into. K[sub]3[/sub][Cr(C[sub]2[/sub]O[sub]4[/sub])[sub]6[/sub]].
Chemical analysis of chromate untransformed made by photocolorimetric and titrimetric methods, confirming 99% extraction degree.
The IR spectrum confirmed the structure and composition of chromium oxalate complex.
By reciprocal treatment it was realised a subproduct and the cleaning in the same time waste waters with chromate anion, oxalic acid and sulphuric acid
REFERENCES
Grunwald, E. and Oniciu., L., Galvanotechnics, Scientific and Encyclopedic Publishing House, Bucharest, 1980
Dash. P., Srinivasa Rao. K, Sarani. D., and Roy. P., Jnl. of Chem. Techn. and Biotechn., (77), pp 1107- 1113, 2002
Bazan J. K., Bisang J.M., Jnl. Appl. Electrochem., ( 34). pp 50-54, 2001
Macarovici C., Inorganic quantitative chemical analysis, Romanian Academic Publishing House, Bucharest, 1979
Gavris G., Environment polluted chemistry, Publishing Univ. House, Oradea, 2003
Olaru R., Suteu D., and Paduraru C., The utilization of celulozic materials for waste water deppolution, Chem. Jrn, (7 ). pp 123-128, 1998
Gavris G., Iovi A., and Sebesan M., Stady of the cleaning process of the waste water with zinc ions content, Chem.. Bull. Politehnica Univ.Timisoara, 50 (64), pp. 166-168, 2005
Georgeta GAVRIS1*, Anda PETREHELE1, Sanda BOTA1, Ioana TOMULESCU1, Vasilica MERCA1
1University of Oradea, Faculty of Science, Department of Chemistry, Str. Universitatii, no.1, Romania
* Correspondence: Georgeta Gavris, University of Oradea , Faculty of Sciences, Univeersity street, no.1 Oradea, Romania, email: [email protected]
Received: march 2008; Published: may 2008
You have requested "on-the-fly" machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Show full disclaimer
Neither ProQuest nor its licensors make any representations or warranties with respect to the translations. The translations are automatically generated "AS IS" and "AS AVAILABLE" and are not retained in our systems. PROQUEST AND ITS LICENSORS SPECIFICALLY DISCLAIM ANY AND ALL EXPRESS OR IMPLIED WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES FOR AVAILABILITY, ACCURACY, TIMELINESS, COMPLETENESS, NON-INFRINGMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Your use of the translations is subject to all use restrictions contained in your Electronic Products License Agreement and by using the translation functionality you agree to forgo any and all claims against ProQuest or its licensors for your use of the translation functionality and any output derived there from. Hide full disclaimer
Copyright "Vasile Goldis" Western University Arad, Romania 2008