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8Journal of Siberian Federal University. Engineering & Technologies 8 (2013 6) 903-910
УДК 581.522.5
Sorption Cleaning of Galvanic Wastewater from Fe Ions (II), (III) and Reuse of Sorbent Ipi-T
Elena G. Filatova*, Olga I. Pomazkina and Vladimir I. Dudarev
National Research Irkutsk State Technical University 83 Lermontova, Irkutsk, 664074 Russia
Received 13.06.2013, received in revised form 28.08.2013, accepted 20.10.2013
The sorption method of wastewater cleaning from ions of Fe (II) and (III) using carbon sorbent IPI-T synthesized in the Irkutsk State Technical University. Particular attention is paid to the regeneration of the carbon sorbent saturated with ions of Fe (II) and (III),by the chemical treatment method. Was studied the reuse of the sorbent for the purification of galvanic wastewater.
Keywords: water treatment, galvanic wastewater, adsorption, carbon sorbents, Fe ions (II) and (III).
1. Introduction
One of the most pressing environmental problems of engineering companies, having in its production cycle electroplating processes, the problem is a deep cleaning of waste water from heavy metal ions. Water treatment of Fe ions (II) and (III), is traditionally carried out by transferring them into water-insoluble compounds, which are then removed by sedimentation, flotation, filtration and other methods of separation of solid and liquid phases. Translated into the solid phase is mainly carried out by introducing alkali with the formation of hydroxides, hydroxo-carbonates, carbonates. However, the use of reagents for the withdrawal of metal ions from the liquid phase leads to an increase saline in a purified water and makes it difficult to use in circulating water systems businesses. The priority method of neutralization of waste water from heavy metal ions are the physico-chemical, which include electrochemical and sorption methods of wastewater treatment. Sorption methods are one of the most effective methods of disposal of waste water from heavy metal ions.
Objective: To study the main regularities of the sorption process of cleaning galvanic wastewater from Fe ions (II) and (III) by using carbon sorbents IPI-T, synthesized in the Irkutsk State Technical University [1].
2. Experimental procedure
Carbon adsorbents IPI-T is a black granules of irregular shape with an average particle size of from 2 to 5 mm, with a specific surface area 480 m2/g, total pore volume is 0,65 cm3/g, micropore volume - 0,28 cm3/g.
© Siberian Federal University. All rights reserved
* Corresponding author E-mail address: efila@list.ru
As objects of investigation useda waste water containing from 1 to 3i mg/l of Fe ions (II) and from 0 Co 36,b mg/l of Fe ions litl). It ts knewn thai the sons of Fe (il) ate stable in water with low oxygen coFtent. lit ths coctamtnated waate waSar of distolved oxygen, or foes not exist at all, or its cnncerbnetion doas nt)t eacoeF 0,bjC mgtt. Tin cc^n(iej^ts;jj;ten of Fe liihS etas controlled by a standard peamanganatsmetrrc quantitativeenalysis [2], the rtladivtmeaaucemenl aeror did not exceed ±0,1%. The cooceniealion of Fe (III) was controlled the spectrophotometric method of analysis using the
Toectudye° ihe adsorfrtion ^^c>ocn}ki^sit1^^ sosbenj winhrcspect totiic.ons of Fe (II) and (III) in ¡static conations was j3i^/^^i^]o^e^uo0n^iso^]ei^i^miifcd o^rnbjtcc^isst^i;it^r?i^dlsori^t;ion. We used the method ofvajMilepontions Ie . lg, 0,n5g,0,a g,0,en gland censradtcancbntration. Kinetic experiments rn sSallc conditksns dstermsned ttto t^jntis je fstabhsh ecui[tbtiumin ilje sgetem carbon adsorbent -sciution of meta^dt. Themagmtnde of edsotptionmstatieconditinditA, mmol/kg) was calculated bythcformula
A = c" -Va m
where ct anear n ioitial and final metal concentration in solution, mmol/l; V - volume of solution, l; m is parjionnf jc^si)ebent( kg.
Dynamic aceMly aO tlaa soibent wat ^nasг^l^teri^(td bga ^ete time from the beginning of the adsorptive transmission to the «breakthrough», ie till appearance him after sorbent layer. The process of sorption under dynamic conditions was carried out in a column with an inner diameter of 16 mm. The column was filled with the sorbent in an amount of 10 g (layer height - 12 cm). The ojimumflowratc enOheadceraare through the sosbent teyer watSt-iSml. m in, which corresponds to a tinear velocttnlntilcIndustria/ oomditions of 1,5-2,0 m/h.
Thtdegree of decor°tibnof melak wnsealcuiated by the formula
c ■ V e„ =—d- ■l/Z/o M m ■A
where cd - the concentration of metal in the passed volume, mg/l, Vd - the passed volume, l; m - portion ofadsorbent,g; A - the capacityoftheadsorbent, mg/g.
3. Results and discussion
We found that the maximum adsorption of ions of Fe (II) by carbon sorbents IPI-T happened in a weakly acidic medium at pH = 3.9 [6]. The maximum value of the adsorption of Fe (III) from wastewater is achieved at pH = 1.79 [7]. Further study of the sorption in the dynamic and static conditions was carried out at the optimum pH.
In Fig.1. shows the adsorption isotherm of Fe (II), constructed from experimental data obtained under static conditions at a temperature of 293K.
As can be seen from Fig. 1., the shape of the curve corresponds to the adsorption of a multilayer or poly-molecular, adsorption. In Fig. 2. shows the adsorption isotherm of Fe (III) at a temperature of 293K.
From Fig. 2. shows that the shape of the adsorption of ions of Fe (III) is similar to the form of isotherms for Fe ions (II). For multilayer adsorption isotherms can be applied the BET theory. The isotherm equation of BET adsorption:
Cp. niinol/ I
Fig.2. Adsorption isothermofFe(III): 1 -thecurve of adsorption 2 - desorption curve
A = _ C • (c/c0)
(1 - c / c0H1 + (C-1)(c / Co)]
wfere A -thevalueofadsorption,mmol/kg; - ultimate ad^sorption capacity of the monolayer, mmol/kg;V - cooriantfota gtvenidsotrtsor system, directly delated ta t^O^e heat and entropy of ad-rocation; a, c0 - the equflibriumandiniiiaic orpeeiratton of Fe (II) cid (III) , mmol/t. Theeqroation of t^Iain aPsorpiion it line ar form:
c/c0 1 C-1 ,
-• c / c„.
g(1 - c/c0) g„-C g„ • C
The adsorption isotherms of Fe (II) and (III) were constructed for the study of IPI-T sorbent (Fig. 3.)using the equationof theBET adsorptioninthe linear form.
- 905 -
c / Cp
0.7 0.6 0.5
0.5
h -a
Fig;. 33. horption isotherms of the linear form of BET equation 1 - for the ions of Fe (II); 2 - ions to Fe (III)
Table 1. BET equation constants for the study of IPI-T sorbent
Ions Thf equation C/C° = /(c/c°) Max. sorption capacity of the monolayer A„ mol/kg Constant C10-3 Coefficient of corellatio n
Fe ( II) c/C° = 0,186 (c/c„) + 0,006 A(1 -c/c°) V 00)52 3?2>,0 0,9850
Fe (III) c/c° -0,036 (c/c°) + 0,012 A(1 -c/c°) V 0,021 41,0 0,9333
Fro m the linear dependence shown in Fig. 3., using the tangent of slope of the straight lines and the value of segments crossed with thi straight axis, was measured maximum sorption capacity of the monolayer A„ and a constant C (Table 1).
In connectio n with the fact that the constant C in equatio n BET is the ratio of two equilibrium constants C=£/kf, ir can also be regfrded at the equilibrium constant, ie to calculate the ¡standard Gibbs energy can be utse;tl equation
AG0C = -R Tln C m - R-T-ln k/k2.
Thus, for ions of Fe (II) AG°C= - 25,7 kJ/ mol, and for the ions of Fe (III) AG°C = - 20,5 kJ/ mol, AG°C reflects the standard Gibbs energy of pure adsorption as a result of interaction between the adsorbate and the surface of the adsorbent.
In the course of the work performed studied the effect of temperature on the sorption of ions of Fe (II) and (III) IPI-T sorbent, the results presented in Fig. 4. and 5.
T. JlOlll
Fig. 4. Kinetic curve;s ofsorption of Fe (II)
From Fig. 4. shows that with increasing temperature is increased the adsorption of Fe (II). However, physical adsoeption is exothermic and reversible, and the increase in temperature should lead to a decrease in speed, liowever, the experimental data indicate that the temperature increases the rate of process. Consequently, the adsorption of ions od Fe (II) takes place hctivaeed adsorption. "We found that ehe maximum adsorption occurs at 343 K, a further increase in temperature leads to a decrease in the adsorption «if ions of Fe (II) sorbent ofIPI-T.
From Fig. 5. sFows that with increasing temperature at first is an increase in the adsorption of Fe (III)a as the heat always helps to speed up the establishment of equilibrium in the syseenn. Further, when the temperature incdedee adsorption, corresponding io the equilibrium state decreases. Thus, the kinetic curves of adsorption of ions of Fe (III) at different temperatures cross each other, as ahown in Fig. 5.
The obtained temperature dependence of the adsorption of ions of Fe (II) and (III), confirms the fact that the Fe hydroxide (II) is a strong base, so the ions of Fe (II) is characteristic of activated
adsorption. Hydroxide, Fe (III), is a weak base, it is reflected in the fact that the salts of Fe (III) is strongly hydrolyzed and Fe ions (III) is characterized by physical adsorption.
In this paper we studied the adsorption of Fe (II) and (III) in dynamic conditions. Established that the protective effect of IPI-T sorbent for sorption of Fe (II) is two hours, then within an hour the concentration of ions of Fe (II) of the adsorbent layer remains within the MPC. The time of the protective action of IPI-T sorbent for sorption of Fe (III) was slightly less than two hours. The time, during which the concentration of the substance in the filtrate changes from the adsorbate concentration at an acceptable breakthrough, corresponding to the concentration of Fe (II) and (III) within the MPC to the initial concentration was about 6 hours.
4. Desorption and reuse of sorbents
Sorption method for the extraction of metals economically rational only if used the repeated use of sorbents. Therefore, the regeneration of carbon sorbents is one of the main issues arising from the sorption method of extraction of metals from waste water. The purpose of regeneration is, on the one hand, the desorption of adsorbed ions, or the destructive removal and, on the other hand, the recovery of the adsorption capacity of the sorbent.
In this paper we studied the regeneration of the carbon sorbent IPI-T, saturated with Fe ions (II) and (III), by the method of chemical treatment. Capacity of the saturated sorbent IPI-T for Fe (II) was 3,41 mg/g, and the Fe (III) - 1,16 mg/g . The process of desorption of the saturated sorbent IPI-T ions of Fe (II) and (III) (mass portions - 0,5 g) was carried out with solutions of hydrochloric acid (acid volume - 40 ml) of various concentrations under static conditions, regeneration time was 120 minutes, the results in Tables 2.
The data in Table. 2 that the maximum desorption of ions of Fe (II) occurs when using 0,56 M hydrochloric acid solution, and the maximum desorption of ions of Fe (III) - by using 0,74 M solution. Since the desorption process is endothermic, then it should be lead at an elevated temperature. An increase in temperature is an effective means of increasing the depth of the desorption of carbon
Table 2. Results of regeneration IPI-sorbent with hydrochloric acid at T 298 K
Dilution HCl Concentration HCl, Ions of Fe (II) Ions of Fe (III)
% mol/l Concentration in eluate, mg/l Degree of desorption, % Concentration in eluate, mg/l Degree of desorption, %
1:2 12,0 3,2 18,3 21,3 3,4 31,6
1:4 7,2 1,9 19,4 21,1 6,1 56,3
1:6 5,1 1,4 20,0 21,8 6,4 59,2
1:8 4,0 1,1 18,8 20,6 7,5 69,5
1:10 3,3 0,87 21,1 23,1 7,6 70,5
1:12 2,8 0,74 21,7 23,7 9,2 85,6
1:14 2,4 0,64 24,0 26,2 7,7 71,5
1:16 2,1 0,56 24,3 26,5 7,3 68,0
1:18 1,9 0,51 22,9 25,0 6,2 57,7
1:20 1,7 0,46 22,3 24,3 4,1 37,7
1,5 т. hour
Fig. 6. The curves of desorption of ions of Fe (III) by carbon sorbent IPI-T
sorbents. The process of desorption of the carbon sorbent; IPI-T was performed in the temperature range 303-3353 K using a 0,74 M solution o°Fe (fII), the reeults are shown in Figure 6.
From Fig. 66. it follows that the degree of desorption of ions Fe (III) at 353K up to 99,6%. Carrying four cycles «sorption-desorption» showed a reduction of sorption activity of the carbon sorbent IPI-T for about 4%.
55. Conclusions
1. Was established the possibility of galvanic treatment of Fe (II) and (III) using the carbon sorbent IPI-T synthesized in the Irkutsk Stad3 Technical University.
2. In the study of adsorption in static conditions, was defined5 the liimited adsooption capacity of monolayer nS carbon sorbent IPI-T by the sorption isotheems of the linear form of IBET equation: for the ions of Fe (II) Al = 0,052 mmol/kg; fof ions ofFe (dII) Ad = 0,021 mmol/kg.
33. In the -tudy of adsorption under dynamic; conditionsl it wf s 3ound the protective ed3ect of IPI-T sorbent foa tire sorption of ions of Fe (II), ie two hours, -hen within af hour the concenteation of ions of Fe (II) of the adsorbent layer remains within the MPC. The time of the protective action of IPI-T sorbent for sorption of Fe (III) was slightly less than two hours.
4. The optimum concentration of acid to regenerate the carbon adsorbent IPI-T: for the extraction of Fe ions (II) is better to use 0,56 M solution of hydrochloric acid for the extraction of Fe (III) - 0,74 M solution.
5. Desorption, using the optimum concentration of hydrochloric acid, saturated with carbon sorbent IPI-T ions of Fe (III) at 353 K is 99,6%. Carrying four cycles «sorption-desorption» showed a reduction of sorption activity of the carbon sorbent IPI-T for about 4%.
References
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Сорбционная очистка гальваностоков от железа (II), (III)
и повторное использование сорбента ипи-Т
Е.Г. Филатова, О.и. помазкина, В.и. Дударев
Национальный исследовательский Иркутский государственный технический университет, Россия 664074, Иркутск, Лермонтова, 83
Изучен сорбционный способ очистки гальвоностоков от ионов железа (II) и (III) углеродным сорбентом ИПИ-Т, синтезированным в ИрГТУ. Особое внимание уделено регенерации углеродного сорбента, насыщенного ионами железа (II) и (III) методом химической обработки. Изучено повторное использование сорбента для очистки гальваностоков.
Ключевые слова: очистка воды, водоподготовка, гальваностоки, адсорбция, углеродные сорбенты, ионы железа (II) и (III).
