Removal of CoII And SeVI from Raw Metal and Glass Industry Wastewaters Using Nano-Sio2Zro2-Calcium A
* Author to whom correspondence should be addressed.
Sigma Journal of Engineering and Natural Sciences 2018, Vol. 36, Issue 1, pp. 63-74; doi.org/10.62051/ytu.sigma-journal-of-engineering-and-natural-sciences-removal-of-coii-and-sevi-from-raw-metal-and-glass-industry-wastewaters-using-nan
Abstract
Keywords: Co(II); Se(VI); Metal Industry Wastewater; Glass Industry Wastewater; Adsorption; Nano-SiO2 / ZrO2-Calcium Alginate Aerogel; Reuse; Cost.
1. Introduction
Se is found in the effluents in the form of selenate (SeO42-) and selenite (SeO32-) from oil refineries in addition to the industries of glass production, semiconductors [1]. Cobalt, a natural element present in certain ores of the Earth’s crust, is essential to life in trace amounts. It exists in the form of various salts. Cobalt has both beneficial and harmful effects on health. Important natural sources of cobalt in the environment are soil, dust and sea water. Cobalt and its salts are used in nuclear medicine, in semiconductors, in painting on glass and porcelain and electroplating as a catalyst for organic chemical reactions. The permissible limits of cobalt in the irrigation water and livestock watering are 0.05 and 1.0 mg/dm3, respectively (Environmental Bureau of Investigation, Canadian Water Quality Guidelines). Adsorption studies have been utilized to understand the mobility and bioavailability of selenium in diverse systems, e.g. aluminium oxide [2], manganese nodules [3], [4], activated carbon [5], [6] and magnetite [7]. Silica (SiO2), one of the most common oxide materials, has excellent insulation, high chemical stability, low thermal-expansion coefficient and low thermal conductivity [8]. SiO2 glass has no grains with brittle uniform microstructure. This characteristic prevents further application of SiO2 for structural usage. Zirconium dioxide (ZrO2) has high thermal expansion coefficient and excellent corrosion resistance [9]. Owing to the large surface area of ZrO2, controllable pore size, and easy *
Corresponding Author: e-mail: sevil.akcaglar@deu.edu.tr, tel: (232) 301 92 36 / 19236 63
functionalization [10], mesoporous materials have opened several new avenues. Hydrogels are also promising candidates for many other applications in which small pores, such as micropores (pore size < 2 nm) and mesopores (2 nm < pore size < 50 nm), result in a high porosity and surface area responsible for adsorption [11]. SiO2 aerogels match these conditions because they are highly ordered mesopore structures, showing large surface area (360-860 m2/g) and pore volume (0.36e2.9 1 cm3/g) [12]. High surface area and high porosity are the major requisite features including catalysis [13], adsorption and environmental cleanup [14], energy storage devices [15], and water repellant coatings [16] to name only a few examples for ZrO2 / SiO2 nano composite. Owing to the abovementioned properties, environmental remediation feature of aerogels is of those recent rapidly growing and high-performance applications in energy related fields. The environmental remediation of aerogels is quite a matured field and could be conferred to air cleaning such as CO2 adsorption from atmospheric air, industrial and municipal effluents and adsorptive removal of volatile organic contaminants and, to the water treatment process for adsorption of oil and hazardous organic compounds and heavy metal ions. The above-mentioned contaminants are of major pollutions causing the serious environmental problems such as global warming and hazards for human health. In the current study, the feasibility of adsorbing of Selenium (VI) and Cobalt (II) from glass and metal industry wastewaters by nano SiO2 / ZrO2-Calcium Alginate Aerogel composite produced under laboratory conditions was investigated for the first time. The physicochemical properties of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite were investigated by SEM, BET and Nitrogen adsorption / desorption isotherms. The effects of increasing Calcium Alginate Aerogel Concentrations in the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite (2, 4, 6 mg/L), effects of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite concentrations(1, 2, 3, 4, 5, 6 and 7 mg/L), effects of contact time (30, 45, 60, 70 and 80 min) and effect of pH (2, 4, 6, 7 and 8) on the adsorption capacities of Se(VI) and Co(II) were investigated.
2.1. Preparation of Nano–Composites
2.1.1. Preparation of Nano-SiO2 / ZrO2-Calcium Alginate Aerogels The preparation of SiO2 / ZrO2-Calcium Alginate Aerogels mainly includes three steps [17]:
1. Synthesis of SiO2 sol: 5.30 g of Polyethylene glycol (PEG) was dissolved in 30 mL
hydrochloric acid (0.02 M). Then, 15 mL of Tetraethoxysilane (TEOS) was added into the resulting solutions with rapid stirring for 45 min, and 20 mL of Propylene oxide (PO) was added into the mixture. This mixture was transferred to the oven at 40 0C.
2. The preparation of ZrO2 started with mixing of 0.17 Polyoxyethylene (PEO), 1.80 g
ZrOCl2.8H2O, 2.6 mL deionized water and 2.8 mL ethanol during 160 min. Then 0.48 mL of PO was slowly added in the mixture. The resulting mixture was stirred for 7 min and transferred to the incubator at 80 0C. 3. ZrO2 was added to SiO2 by stirring to form homogeneously distributed Nano-SiO2 / ZrO2 composite. Then, three different calcium alginate concentrations (2.0g, 4.0 g and 6.0 g) were incorporated into the Nano SiO2 / ZrO2 composite by stirring for 20 min. This Nano composite was incubated in an incubator at 40 0C. After production of an aerogel, the liquid solvents were removed by solvent exchange at 40 0C. The produced Nano-SiO2 / ZrO2-Calcium Alginate Aerogel were dried at 40 0C [17].
2.1.2. Characterizatio n of Nano-SiO2 / ZrO2-Calcium Alginate Aerogels The micrograph was recorded by the scanning electron microscopy (SEM) (SU-70) with an accelerating voltage of 3.0 kV. The surface area, average pore diameter and pore volume of the products were studied by nitrogen adsorption and desorption analysis (AUTO SORB-1-C). An UV Visible Spectrophotometer (DU800) was used for obtaining the absorption spectra from 200 to 500 nm. Ultraviolet and Visible Spectrophotometry (UV Vis) is used the samples for testing. The phases of waste forms were characterized by X-ray diffraction (X' pert PRO) method through determining the existence of different characteristic peaks. The diffraction data were collected over the angle range 100-900 with a step size of 0.020. The back-scattered scanning electron microscopy (Hitachi S-3700N) was coupled with Energy Dispersive Spectroscopy (EDS) to investigate distribution of elements and microstructure of the waste forms [17].
2.2. Analytical Procedure
2.2.1. Se(VI) Measurement Method A volume of 1 mL of was digested with 5 mL HNO3 and H2O2 using glass industry and metal industry, separately as follows: 20 min up to 250°C and 15min at 250°C. After cooling down the digests were diluted with 1% HNO3 and analyzed by ICP-MS. Quantitation was achieved by 5 point external calibration (standards from 0.1 mg/L to 4 mg/L, correlation coefficient R2 = 0.9998, limit of linearity 105 mg/L) and validated by the analysis of Se(VI) reference material. The limit of detection for Se(VI) was 0.39 × 10− 3 mg/L. Mobile phases for anion exchange liquid chromatography (HPLC-ICP-MS analysis) were prepared by dissolving an appropriate amount of ammonium acetate in deionized water to obtain the required concentrations at pH = 4.7: i) 5 mmol/L (solvent A) and ii) 150 mmol/L (solvent B). The mobile phase flow rate was 1 mL/min at 22 °C. The solutions were filtered and degassed before the use. The injection volume was 100 μL. Compounds were eluted with the increasing linear gradient from 0%–100% of solvent B within 21 min. The chromatograms were obtained with Se(VI) detection. In order to perform identification by ESI-MS/MS eluates were collected to vials at times corresponding to the retention times of previously registered selenium signals. The volumes of collected fractions were various depending on the selenium registered peak width. 2.2.2. Co(II) Measurement Method A PG-990 (PG instrument Ltd., United Kingdom) atomic absorption spectrometer equipped with deuterium background correction and cobalt hollow cathode lamp was used for the determination of cobalt at a wavelength of 240.7 nm. A Hettich centrifuge (Model Universal 320R, Germany) was used for centrifuging. The pH values were measured with a pH-meter supplied with a glass-combination electrode. 50 mL sample or standard solution containing Co(II) in the concentration range of 0.1–5 mg/L and 2.0 × 10−3 mol/L HCl was adjusted to pH 3.0 (±0.2) and was poured in a screw cap conical-bottom glass centrifuge tube. 0.5 mL of 2Methylimidazole (Hmim), Tetrafluoroborate (BF4) was added into the sample solution and the tube was manually stirred to ensure complete homogenization of the aqueous sample. Then, 4.0 mL of isoelectronic with sulfur hexafluoride, SF6 and the Sodium hexafluorophosphate (NaPF6) solution (0.5 mol /L) was quickly added, followed by the formation of a turbid solution. In order to accelerate phase separation, the cloudy solution was centrifuged for 10 min at 3000 rpm. As a result, the phase settled at the bottom of the centrifuge tube. The aqueous phase was then separated completely by a syringe. In order to reduce the viscosity of the extract in the tube was made up to 1.0 mL by adding ethanol. The resultant solution was introduced into the flame by conventional aspiration [18]. 65
2.3. Co(II) and Se(VI) Concentrations in the Raw Glass and Metal Industries
The Co(II) concentrations in the raw metal concentrations varied between 1, 1.5, 2.0 and 2.5 mg/L while the Se(VI) concentrations in glass industry wastewater were 0.4, 0.8, 1.2 and 2.5 mg/L, respectively.
2.5. Statistical Analysis
Regression analysis is used to understand which among the independent variables are related to the dependent variable, and to explore the forms of these relationships. Alpha (α) level is the significance of the Analysis of Variance (ANOVA) statistic. In the study α was accepted as 0.05. F value of the analysis was performed using MS Office 2010 Excell program.
3.1. Characterization of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite with SEM
The SEM morphologies of the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite are shown in Fig. 1a and 1b for 2 mg/L and 4 mg/L Calcium Alginate Aerogel concentrations, respectively.
Figure 1. SEM images of 5 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite with 2 mg/L (a) and 4 mg/L (b) Calcium Alginate Aerogel concentration The SEM images showed that the silica aerogels possess spherical primary particles aggregates and porous structure. These characteristics enable the SiO2 become a good skeleton for the composite aerogels. Fig. 1a and 1b show that the morphologies of 6 mg/L Nano-SiO2 / ZrO2Calcium Alginate Aerogel composite with 2 mg/L Calcium Alginate Aerogel are different due to their not similar calcium alginate contents. The spherical primary particles in Fig 1a, the NanoSiO2 / ZrO2-Calcium Alginate Aerogel composite are smaller than silica aerogels and the pore diameter is decreased with the increasing contents of calcium alginate (diameter data not shown). There are mainly two possible causes for this phenomenon: Firstly, the incorporation of ZrO2 into the SiO2 lattice produced new bonds in the aerogels [17]. Secondly, calcium alginate filled a part of the pores with the increasing contents [4], [9]. Calcium alginate filling the pores was explained by EDS analysis of Ca ( Fig. 2). It was found that crystalline phases were constituted by the all components of the nano composite. SiO2 was monitored in the background of the Fig.2. The grey, and semitransparant domains are Ca2SiO4 and ZrO2 coated with SiO2.The Calcium Alginate 66
Aerogels (a), Si (b), Ca (c) and Zr (d) are illustrated in Fig. 2. The EDS analysis results showed that ZrO2 and SiO2 were incorporated to Calcium alginate and this nanocomposite was stable.
Figure 2. EDS analysis of Ca2SiO4 aerogel (a), Si (b) Ca (c) and Zr (d) in the SiO2-ZrO2-Calcium Alginate Aerogels
3.2. Nitrogen Adsorption / Desorption Isotherms of the SiO2-ZrO2-Calcium Alginate
Aerogels for Co(II) and Se(VI) The nitrogen adsorption / desorption isotherms of the SiO2 / ZrO2-Calcium Alginate Aerogels are showed in Fig. 3a for Se(VI) and Co(II). The maximum volume adsorbed was found as 110 cc/g for Se(VI) while the maximum volume adsorbed was 85 cc/g for Co(II) at 1 P/Po value.
100 60 40 20 0 0 0,1 0,3 0,5 0,7 0,8 0,9 1 P/Po Volume adsorbed for Se(VI)( cc/g) Volume adsorbed for Co(II)( cc/g)
150 100 50 0 0 5 10 20 25 30 45 50 60 Time (min) Adsorption capacity ( mg/g) for Se (VI) Adsorption capacity ( mg/g) for Co (II)
(a) (b) Figure 3. Nitrogen adsorption / desorption isotherms of the SiO2-ZrO2-Calcium Alginate Aerogels for Se(VI) and Co(II)(a); BET analysis of Se(VI) and Co(II)(b)
3.3. BET Analysis
The adsorption capacity of Se(VI) and Co(II) on SiO2 / ZrO2-Calcium Alginate Aerogel composite versus contact time is represented in Fig. 3b. The maximum adsorption capacity of Se(VI) reached 275 mg/g (with a maximum adsorption yield of 98) (data not shown) after 45 min adsorption time. The maximum adsorption capacity of Co(II) was 225 mg/g after 45 min. The adsorption capacity was low at the beginning of adsorption times (70 and 85 mg/g after 10 min for Co(II) and Se(VI) respectively. The adsorption capacity of two metals increased as the time elapsing, it increased quickly in the initial stages up to thirty minutes of hours, and then increased after 45 min at subsequent contact time. Then it remained constant. The faster initial adsorption rate due to the existence of a good deal of active sites is available for Se(VI) and Co(II) ions bindings. With the increase of contact time, the adsorption capacity did not change because of the vacant surface sites of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite were occupied and formation of repulsive forces between the Se(VI) and Co(II) ions on the composite surface and in the liquid phase as reported by Caiping, 2010 [19]. BET analysis indicates that the products possess high surface areas with 462.10 m2/g for Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite with 2 mg/L Calcium Alginate Aerogel concentration in the adsorptions of Se(VI) and Co(II) ( Table 1). The pore diameter is high in the nano composite containing 2 mg/L calcium alginate aerogel concentration compared to nano composite having 4 mg/L calcium alginate aerogel concentration. The pore diameter and the pore volume of nano composite having 2 mg/L calcium alginate aerogel concentration were 8.60 nm and 0.5 cm3/g pore volume. The nano composite with 4 mg/L Calcium Alginate Aerogel concentration has lower surface area and pore diameter. Table 1. Surface physical parameters of SiO2/ZrO2-Calcium Alginate Aerogel with 2 mg/L, 4 mg/L and 6 mg/L Calcium Alginate Aerogel concentration Samples
2 mg/L* 462.10 4 mg/L* 420.80 6 mg/L* 233.44 * Calcium Alginate Aerogel concentration 68
3.4. Effects of increasing Calcium Alginate Aerogel Concentrations in the Nano-SiO2 / ZrO2Calcium Alginate Aerogel Composite on the Removals of Co(II) and Se(VI)
As the Calcium Alginate Aerogel Concentrations were increased from 2 mg/L up to 6 mg/L and equilibrated for 6 hours, both Co(II) and Se(VI) adsorption yields decreased( Figure 4a). The maximum Co(II) and Se(VI) adsorption removals were obtained at a Calcium Alginate Aerogel Concentration of 2 mg/L. The maximum adsorption yields for Se(VI) is higher than Co(II). This shows that the removal of Co(II) as a function of the Calcium Alginate Aerogel concentration.
Calcium Calcium Calcium alginate alginate alginate aerogel conc aerogel conc aerogel conc (2 mg/l) (4 mg/l) (6 mg/l)
Nano-SiO2 /ZrO2 Calcium Alginate Aerogel concentration (mg/l)
Figure 4. Effects of increasing Calcium Alginate Aerogel concentrations in the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite on the removals of Co(II) and Se (VI)(a) Effects of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite Concentrations on the Removals of Co(II) and Se(VI) at 2 mg/L Calcium Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite Alginate Aerogel concentration(b) A multiple linear relationship between maximum adsorption yields of Se(VI) and Co(II) and Calsium Alginate Aerogel concentrations (from 2 mg/L to 4 mg/L and 6 mg/L ) was obtained (R=0.89) and this regression was significant (ANOVA p=0.0009<α (0.05) and F=1.10).
3.5. Effects of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite Concentrations on
the Removals of Co(II) and Se(VI) The studies were performed at a 2 mg/L Calcium Alginate Aerogel concentration since in the previous study the maximum adsorption yields of Se(VI) and Co(II) were obtained with this adsorbent concentration. As the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite concentrations were elevated from 1 mg/L up to 4 mg/L; the the adsorption yields of Se(VI) increased from 57% up to 98% (4b). Further increase of composite concentration to 5, 6 and 7 mg/L did not affect the Se(VI) adsorption yields. The adsorption yields remained as in 4 mg/L. 69
Similar results was found for Co(II). The maximum adsorption yields for Co(II) was obtained at 4 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite concentration. Increasing of the composite concentration did not affect the adsorption yield of Co(II). These results showed that the adsorption yields of both metals depends to the nano-composite concentration up to 5 mg/L. This may be due to the high ion exchange capacity of the Nano-SiO2 / ZrO2-Calcium Alginate Aerogels [4], [9]. The experimental results revealed that Co(II) and Se(VI) adsoption yields increases up to the optimum dosage beyond which the removal efficiency has no change with the Nano-SiO2 / ZrO2-Calcium Alginate Aerogels dosage as reported by Somiya et all., (1988) and Matias et all., (2015) [20], [21]. As expected, the equilibrium concentration decreases with increasing composite doses for a given initial composite concentration, because for a fixed initial concentration, increasing composite doses provide greater surface area or adsorption site sup to a optimum concentration as reported by Somiya et all., (1988) and . Matias et all., (2015) [20], [21]. A multiple linear relationship between maximum adsorption yields of Se(VI) and Co(II) and Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite concentrations up to 5 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel Composite was obtained (R=0.86) and this regression was significant (ANOVA p=0.007<α (0.05) and F=1.30). Further increase of Nano-SiO2 / ZrO2 Calcium Alginate Aerogel Composite concentration did not affect both Co(II) and Se(VI) adsorptions.
3.6. Effects of Contact Time on the Adsorption Capacities of Co(II) and Se(VI)
The studies were performed at 2 mg/L Calcium Alginate Aerogel Concentration at 5 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite to determine the effects of adsorption time on the adsorption yields of Se(VI) and Co(II). Fig. 5a shows the effect of contact time on the adsorption capacities of Se(VI) and Co(II) by 5 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel.
200 150 100 50 0 30 45 60 70 80 min min min min min Adsorption time (min) Se (VI) adsorption capacity ( mg/g) Co (II) adsorption capacity ( mg/g)
pH Se (VI) adsorption efficiency (%) Co (II) adsorption efficiency (%)
Figure 5. Effects of Contacting Time on the Adsorption Capacities of Co(II) and Se(VI)(a), Effect of pH on the adsorption efficiency of Se(VI) and Co(II) at 5 mg/L Nano-SiO2 / ZrO2Calcium Alginate Aerogel composite after 45 min adsorption time at pH=6.1(b)
The adsorption capacities of Nano SiO2 / ZrO2-Calcium Alginate Aerogel composite; increases with time and attains equilibrium within 45 min for both metals. The equilibrium time was dependent up to 45 min adsorption. Then, the increase of contacting time did not affect the adsorption capacities of both metals. It was found that Se(VI) adsorption capacity (275 mg/g) was higher than Co(II) adsorption capacity (225 mg/g) after 45 min adsorption time at 5 mg/L composite and 2 mg/L Calcium Alginate Aerogel concentration. The metal uptake versus time curves are monotonously increasing to saturation, suggesting the possible monolayer coverage of metal ions on the surface of the adsorbent up to a contacting time of 60 min. A multiple linear relationship between maximum adsorption yields of Se(VI) and Co(II) and adsorption times up to 45 min was obtained (R=0.89) and this regression was significant (ANOVA p=0.005<α (0.05) and F=1.09). Further increase of contacting time did not affect both Co(II) and Se(VI) adsorption yields.
3.7. Effect of pH on the Adsorption Yields of Co(II) and Se(VI)
The effect of pH on the Co(II) and Se(VI) adsorption on the nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite at a pH between 2.0 and 8 is presented in Fig. 5b. It can be found that the adsorption yields, increased with pH for both metals. The uptake of Co(II) and Se(VI) by Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite increased as the pH increased from 2.0 to 6.1. At higher pH values (7.0 and 8.0) the adsorption efficiency decreased for both metals. Although a maximum uptake was noted at a pH of 7.1, as the pH of the solution increased to >6.1 Co(II) started to precipitate out from the solution. Therefore, the increased capacity of adsorption at pH = 6.1 may be a combination of both adsorption and precipitation on the surface of the NanoSiO2 / ZrO2-Calcium Alginate Aerogel composite. It is considered that Nano-SiO2 / ZrO2Calcium Alginate Aerogel composite had a maximum adsorption capacity at a pH of 6.1, if the precipitated amount is not considered in the calculation. Therefore, the optimum pH for Co(II) and Se(VI) adsorption is 6.1.Similarly, Se(VI) adsorption on the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composites tends to increase with the pH. This is likely attributed to the fact that a lower pH value causes the surface to carry more positively charges and thus would more significantly repulse the positively charged species in solution. Therefore, the adsorption of Se(VI) at lower pH values resulted from an increased repulsion between the more positively charged Co2+ species and positively charged surface sites. Furthermore, at lower pH, H+ ions compete with Se(VI) ions to the surface binding-sites of the adsorbent [19]. The adsorption efficiencies of Se(VI) and Co(II) increased from 43% to 87% and up to 98% as the pH were increased from 2 to 4 and up to 6. In our study adsorption was directly dependent to the pH. For the Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite, the adsorption at pH above 6.0 shows a decreasing trend because of the formation of hydroxyl complexes of cobalt, Co(OH)2 [22] and selenium, Se(OH)2.
3.8. Recoveries of Se(VI) and Co(II)
The adsorption efficiencies in both metals were not reduced significantly after four sequential utilization of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite (Table 2). In this study the adsorption yields of Se(VI) and Co(II) were 99% and 96% in the first utilization. After four sequential utilization of the same Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite the adsorption yields of Se(VI) and Co(II) decreased to 87 and to 83 %, respectively.
Table 2. Sequential treatment of Se(VI) and Co(II) with 4 mg/L Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite concentration, after 45 min adsorption time at pH 6.0, at a temperature of 80 OC and ionic strength 0.009 M Sequential cycles and adsorption yields (%) Parameters For Se(VI) For Co(II)
4. COST Analysis
A cost analysis was carried out for the adsorptions of Se(VI) and Co(II) from 1 m3 glass and metal industry wastewaters at optimum experimental conditions. The total cost of the adsorptions of Se(VI) and Co(II) from 1 m3 glass and metal industry wastewaters were found as 1,62 € and 1,99 €, respectively, at the optimum experimental conditions with Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite (Table 3). 1,10 € and 1,47 € were spent as electricity costs for glass and metal industries for adsorptions Se(VI) and Co(II), while the chemical cost of synthesizing Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite was 0.64 € (Table 3). In this study, the main part of the cost consisted of the electricity. Since the composite namely Nano-SiO2 / ZrO2Calcium Alginate Aerogel composite produced under laboratory conditions can be used four times for adsorptions of Se(VI) and Co(II) with yields as high as 87% and 83% the cost is equal only to electricity consumptions. This reduce the adsorption costs to 0,98 € and 1.35 € for Se(VI) and Co(II).The total adsorption cost reduced by % 38. Table 3. Cost analysis for the treatment of Se(VI) and Co(II) with adsorption Cost Analysis
Treatment of glass and metal industry wastewaters with adsorption process
Electricity cost for rapid stirring in a mixer for 45 min= 0,20 €, Electricity cost for rapid stirring in a mixer for 45 min= 0,37 €, Electricity cost for incubation at an oven at 4 0C =0,40 €, Electricity cost for incubation at an incubator at 80 0C=0,5 €. For preparation of nano-SiO2 sol:
5.30. g of Polyethylene glycol (PEG) = 0,34 € ,
30 mL hydrochloric acid (0.02 M)= 0,02 €. 15 mL of Tetraethoxysilane (TEOS)= 0,05 €, 20 mL of Propylene oxide (PO) = 0,06 € For preparation of nano-ZrO2:
0.48. mL of PO = 0,05 €.
For preparation of Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite Calcium alginate 4.0 g = 0,03 € 1.62 €
Total cost for treatment of Se(VI) from 1m3 glass industry wastewater
1,99 € Total cost for treatment of Co(II) from 1m3 metal industry wastewater
5. Conclusions
The results of this study showed that Se(VI) and Co(II) from glass and raw metal industry wastewaters can be effectively removed with adsorption process. The nano composite namely Nano-SiO2 / ZrO2-Calcium Alginate Aerogel was prepared under laboratory conditions. For maximum Se(VI) (99%) and Co(II) yields (96%) the optimum operational conditions were as follows: Calcium Alginate Aerogel, Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite concentrations, temperature, pH and adsorption time were 2 mg/L, 4 mg/L, 80 oC, 6.0, and 45 min, respectively. It was found that Se(VI) was adsorbed with high yields compared Co(II). The same Nano-SiO2 / ZrO2-Calcium Alginate Aerogel composite can be sequentially utilized for four times with yields as high as 87% and 83%. Therefore the adsorption costs reduced from 1.62 € to
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AKÇAĞLAR, S. Removal of CoII And SeVI from Raw Metal and Glass Industry Wastewaters Using Nano-Sio2Zro2-Calcium A. Sigma Journal of Engineering and Natural Sciences 2018, Vol. 36, pp. 63-74. https://doi.org/10.62051/ytu.sigma-journal-of-engineering-and-natural-sciences-removal-of-coii-and-sevi-from-raw-metal-and-glass-industry-wastewaters-using-nan