Physical-chemical methods of separated decontamination of highly concentrated waste streams from galvanic (electroplating) baths containing nickel, copper, and zinc ions using modified forms of vermiculite have been suggested. At the first stage, decontamination is performed by the method of coagulation using a detergent solution (decontamination degree up to 99%). Thereafter, the produced low-concentration solutions underwent electrochemical treatment with addition of sodium chloride using ruthenium oxide coated titanium anode and cathode. The third stage of extra adsorption decontamination by vermiculite-based sorbents was introduced for nickel- and copper-containing galvanic waste streams. The highest degree of decontamination from nickel and copper was attained using the vermiculite treated by 12% hydrochloric acid and cellulose.

INTRODUCTION

Heavy metals belong to widely spread and highly toxic contaminants. They are extensively applied in various fields of industry. However, despite decontamination arrangements, the contents of heavy metals compounds in industrial waste streams are substantial. Their ability to accumulate in the environment and living organisms and to be transferred along the food chain results in disruption of biochemical processes in a human organism and inevitably makes them potentially hazardous.

At present, the reagent method is the most extensively used one in decontamination of industrial waste streams. Lime and limestone are the most often used precipitators in a majority of countries due to their accessibility and low cost (Mirbagheri 2005; Aziz 2008). Nevertheless, chemical precipitation requires application of large amounts of chemicals to reduce metals concentrations down to acceptable levels. Other disadvantages include slow precipitation (for instance, for heavy metals hydroxides), precipitate aggregation, and huge amounts of formed sludge that requires further disposal. The method of ion exchange allows attainment of virtually complete removal of heavy metals ions with initial concentrations of 100 mg/l from waste streams (Singru 2010; Sayee Kannan et al. 2011). However, the main disadvantage of the method of decontamination by ion-exchange resins is related to their selectivity. In the case of concentrated industrial wastes, ion-exchangers are easily contaminated by organics and other solid particles present in the waste, while ion-exchange processes are highly sensitive to the solution pH.

Recently, the method of flotation treatment has found a wider application in decontamination of waste streams with relatively low contents of heavy metals. However, disadvantages of this very method include poor accessibility and high cost of a majority of high-efficiency flotation agents. The exclusion here is the example when an aqueous solution (60%) of household detergent (soap) is used as a precipitator and a flotation agent for heavy metals ions (Skrylev et al. 1990).

In view of the above, it appears to be of importance to develop physical-chemical methods of decontamination of highly concentrated galvanic baths waste streams with the possibility of separation of metals for further use.

METHODS

The element analysis of the initial vermiculite and its modified forms was carried out using an EDX-800-HS energy-dispersive X-ray fluorescence diffractometer (Shimadzu, Japan) (Table 2).

The carbon content was determined by wet ashing in a mixture of concentrated sulfuric acid and CrO3.

The metals ions concentrations were determined using an АА-6601F atomic-absorption spectrophotometer (Shimadzu, Japan).

The organics contents in wastewaters were determined by the chemical oxygen demand (COD) method.

The samples IR spectra were recorded using a Spectrum-1000 spectrometer (Perkin Elmer, USA) on KBr pellets.

To prepare the detergent solution, a commercial soap of a concentration of 60% was used. 15 g of soap was dissolved at heating in 300 ml of distilled water. The obtained solution of a yellow color was added dropwise to galvanic wastes containing nickel, copper, and zinc cations with concentrations equal to 186.7, 218.37, and 187.92 g/l, respectively. The formed flaky precipitates were filtered, and their weights were equal to 25, 37, and 15 g, respectively. The values of the solutions pH changed only as a result of salts hydrolysis from 6.0 down to 3.0 in dependence on the metal ion concentration.

Adsorption under dynamic conditions was measured in a laboratory column of a height of 15 cm and a diameter of 1.3 cm. Low-concentration solutions containing nickel and copper ions were fed through a stationary adsorbent layer at a constant rate. Samples were taken at each 5th feed.

Vermiculite from Kovdorskoe deposit (Karelia) of the composition (MgFe0.8)Cа0.9Al0.4Si3O11.7H2O was used as a layered silicate.

Preliminary acidic vermiculite modification: 100 g of vermiculite was heated at 120–150 °C until constant weight. Thereafter, it was ground; the fraction of a particle size of 0.10–0.05 mm was poured with 200 ml of 12.5% solution of hydrochloric acid and stirred for 2 days. Then the suspension was filtered and washed with distilled water until neutral reaction. The obtained vermiculite was dried until constant weight (sample 1) and analyzed for contents of main elements.

The vermiculite modification by paper cellulose was performed by dispersing in a cavitator at a frequency of 100 Hz. Acid-pretreated vermiculite (100 g) was placed into a glass of a volume of 800 ml, and, then, 9 g of dry cellulose was added (ash-free filter) and dispersed for 30 min. Finally, vermiculite was filtered and dried at 100 °С until constant weight (sample 2).

Vermiculite modified by cellulose was annealed at 600–700 °C for 3 hours (sample 3).

RESULTS AND DISCUSSION

Galvanic production waste steams to be decontaminated are highly concentrated with the metal concentrations as follows: Ni – 186.7 g/l, Cu – 218.4 g/l, Zn – 187.9 g/l. At first stage of decontamination using detergent solution coagulation (Skrylev et al. 1990), the metal contents in the filtrate decreased down to 10.5 mg/l, 3.5 mg/l, and 6.5 mg/l, respectively. Upon annealing of precipitates produced by coagulation, metals were removed separately, which constitutes a clear advantage of this method.

Despite high degree of decontamination of galvanic wastes upon the coagulation stage, heavy metals ions concentrations did not attain the maximum permissible concentration (MPC). Thus, the second decontamination stage was applied to reduce concentrations of organics (filtrate CODs were from 28.5 mg O2/l for the solution containing Ni ions to 577.5 mg O2/l for that containing Cu ions Cu) and heavy metal ions down to MPC as well as to disinfect wastewaters.

At the second stage, the obtained low-concentration solutions underwent electrochemical treatment for 30 min with NaCl addition and using ruthenium oxide coated titanium anode and cathode. The decontamination results are shown in Table 1.

Table 1

Heavy metal ions contents in low-concentration galvanic waste streams at different decontamination stages

Decontamination stageCNi, mg/lCCu, mg/lCZn, mg/l
Coagulation 10.5 3.5 6.5 
Electrochemical treatment 5.3 1.3 3.5 
Decontamination degree, % 49.5 62.8 46.1 
MPC (SanPiN 2.1.4.1074-010.1 
Decontamination stageCNi, mg/lCCu, mg/lCZn, mg/l
Coagulation 10.5 3.5 6.5 
Electrochemical treatment 5.3 1.3 3.5 
Decontamination degree, % 49.5 62.8 46.1 
MPC (SanPiN 2.1.4.1074-010.1 

As seen from the obtained data, the zinc ions content in wastewaters attained the MPC value, and they do not require extra decontamination.

The third stage of adsorption decontamination under dynamic conditions was added for nickel- and copper-containing galvanic waste streams.

In this extra decontamination, the following sorbents were used (Shapkin et al. 2016): (a) vermiculite treated by 12% hydrochloric acid (sample 1); (b) vermiculite treated by 12% hydrochloric acid and cellulose (sample 2); (c) vermiculite treated by 12% hydrochloric acid and cellulose and annealed at 600–700 °C (sample 3).

IR spectra of the sorbents above are shown in Figure 1.
Figure 1

IR spectra of sorbents under study: (a) vermiculite treated by 12% hydrochloric acid; (b) vermiculite treated by 12% hydrochloric acid and cellulose; (c) vermiculite treated by 12% hydrochloric acid and cellulose and annealed at 600–700 °C.

Figure 1

IR spectra of sorbents under study: (a) vermiculite treated by 12% hydrochloric acid; (b) vermiculite treated by 12% hydrochloric acid and cellulose; (c) vermiculite treated by 12% hydrochloric acid and cellulose and annealed at 600–700 °C.

The bands corresponding to Si-O(Si) and Si-O(Al) bonds vibrations are in the range 1,200–400 cm−1. However, one can state that the band at 1,000–1,007 cm−1 undergoes a shift into the higher-frequency range at vermiculite activation by hydrochloric acid. Positions of the bands in the range 800–400 cm−1 also undergo shifts due to deformation and disruption of four- and six-membered cycles (SiO4 and AlO4) in tetrahedra.

At the vermiculite modification by cellulose (sample 2), low-intensity bands corresponding to C–H bond vibrations in the polysaccharide emerge in the IR spectrum in the range 2,980–2,870 cm−1 (Figure 1(b)). These bands intensities decrease to a minimum upon annealing (Figure 1(c)). However, upon the composite annealing, the carbon content reduces by 55 % (Table 2). The residual carbon (45 %) and the changed composite color allow concluding on an unusual form of the residual cellulose interacting with the silicate surface.

Table 2

Elemental compositions of sorbents under study

NSorbentElements contents, %
SiO2Al2O3MgOCaOFe2O3H2OTiO2C
Initial vermiculite 42.7 11.8 24.5 5.7 8.70 0.14 0.85 − 
Sample 1 89.6 5.2 1.1 1.0 0.30 0.40 0.20 − 
Sample 2 84.5 4.5 1.0 0.9 0.20 0.30 0.10 7.5 
Sample 3 85.6 4.8 1.1 1.0 0.25 0.35 0.10 3.4 
NSorbentElements contents, %
SiO2Al2O3MgOCaOFe2O3H2OTiO2C
Initial vermiculite 42.7 11.8 24.5 5.7 8.70 0.14 0.85 − 
Sample 1 89.6 5.2 1.1 1.0 0.30 0.40 0.20 − 
Sample 2 84.5 4.5 1.0 0.9 0.20 0.30 0.10 7.5 
Sample 3 85.6 4.8 1.1 1.0 0.25 0.35 0.10 3.4 

The vermiculite mesopores filling by cellulose in the absence of heating proceeds simultaneously with interaction of hydroxyl groups by silicon and aluminum atoms with cellulose alcohol groups. The latter is corroborated by disappearance of absorption bands at 961 cm−1, which must correspond to bending vibrations of the – Si-O-H and Al-O-H bonds and by reduction of the intensities of bands in the range 3,600–3,400 cm−1 corresponding to Si-O-H and Al-O-H bonds stretching vibrations.

Extra decontamination of waste streams from nickel and copper ions was carried out under dynamic conditions. Based on the obtained data, dynamic curves for adsorption of nickel and coper ions from solutions by the sorbents under study were built.

The results of studies of the nickel ions sorption dynamics indicate that the longest duration of the column performance until breakthrough characterizes vermiculite treated by 12% hydrochloric acid and cellulose (sample 2) (Figure 2). That is why this sorbent can be recommended for extra decontamination of galvanic waste streams from Ni ions down to MPC values.
Figure 2

Dynamic curves of sorption of nickel ions from aqueous solution for the sorbents: (a) sample 1; (b) sample 2; (c) sample 3.

Figure 2

Dynamic curves of sorption of nickel ions from aqueous solution for the sorbents: (a) sample 1; (b) sample 2; (c) sample 3.

In extra decontamination from copper ions, the optimal variant is related to application of a column filled with vermiculite treated by cellulose and then annealed (Figure 3).
Figure 3

Dynamic curves of sorption of copper ions from aqueous solution for the sample 3.

Figure 3

Dynamic curves of sorption of copper ions from aqueous solution for the sample 3.

CONCLUSIONS

  1. At the stage of coagulation by detergent solution, the degree of waste streams decontamination from nickel, copper, and zinc was about 99.99%.

  2. Electrochemical treatment using ruthenium oxide coated titanium electrodes with subsequent adsorption decontamination on vermiculite treated by 12% hydrochloric acid and cellulose (sample 2) for nickel ions and on vermiculite treated by cellulose and then annealed (sample 3) enable one to decontaminate wastewaters down to MPC values contents.

  3. The suggested method of decontamination of highly concentrated galvanic waste streams allows separated removal of metals from galvanic baths waste streams upon annealing of precipitates produced through coagulation by detergent solution in view of metals further use.

ACKNOWLEDGEMENTS

This work was supported by a grant from The Ministry of Education and Science of the RUSSIAN FEDERATION, Application No. 4.8063.2017/БЧ.

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