Studies on Copper and Zinc Ions Recovery from Aqueous
Solutions by Chemical Precipitation
GEORGETA GAVRIS1, GEORGETA BURTICA2, ALINA CARABAN1, CORNELIU PODOLEANU2, MIHAELA GAVRIS1, DIANA DEM3
University of Oradea, Faculty of Science, 1 Universitãþii Str., 410087, Oradea, Romania
2
Politehnica University of Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, 2 P-þa Victoriei, 300006,
Timisoara, Romania
2
University Politehnica of Timisoara, Faculty of Hydrotechnics, 31 George Enescu Str., 300022, Timisoara, Romania
3
“Directia apelor Crisuri”, 35 Ion Bogdan Str., 410125, Oradea, Romania
1
The study presents a treatment method of waste waters with zinc and copper ions content, in order to
establish the optimum conditions for a high degree of Zn2+ and Cu2+ ions recovery as zinc oxalate or copper
oxalate, due to the low values of their solubility products. The studied parameters were: pH, excess of
reactants, concentration of ions and temperature. The obtained crystalline products correspond to the
formulae: ZnC2O4·2H2O and CuC2O4·0.5H2O, and the recovery degree of metals was around 99% .
Keywords: zinc, copper, oxalate, residual waters, recovery
Waste solutions and scouring waters, with a changeable
content of copper and zinc ions depending on the
technological phase: waste waters, scouring waters,
sluggish waste (galvanic muck), are the result of
automobile industr y, electrotechnics, electronics,
anticorrosive protection using copper, zinc and chrome
coating, synthetic wires and fibers industry, pigment and
zinc oxide-based paints industry, recovery and processing
of rock products [1-4].
Copper and zinc concentrations between 2-30 mg Me2+/
L, allow the treatment of these waste waters by well known
methods – chemical neutralizing with precipitation,
coagulation, ion exchange, cementation and absorption
of various materials with adequate properties [5-7].
In case of copper and zinc residuary solutions such as
exhausted acid copper baths, acid or alkaline zinc baths
[6], waste waters containing zinc and copper from the
synthesis industry, the quantitative chemical analysis has
shown an average content of concentrations of 0.2-7 g
Me2+/L [1,7]. The chemical compounds, based on zinc
and copper, which are found in the waste of the presented
fabrications, are usually: ZnSO4, ZnCl2, Zn(NO3)2, ZnO,
soluble zinc phosphate, CuSO4, Cu(NO3)2, soluble copper
phosphate, along with sulphuric acid, alkaline metal
chloride, sodium hydrate [1,2] .
The present paper presents a study on establishing the
optimal conditions for the chemical precipitation of Cu2+
and Zn2+ ions, as crystallized oxalates, in order to use this
method for recovering treatment of Cu2+ and Zn2+ ions,
from residual solutions.
We have chosen this precipitation method due to the
low values of the solubility products of zinc and copper
oxalates (10-8 order) [8], which assure a high recovery
degree. The precipitation of these crystallized oxalates
represents an advantage compared to the amorphous
precipitates of hydroxids, carbonates, oxyhydroxids [9, 10].
In the paper we have studied the influence of different
parameters: pH of the reaction mass, regeant dose,
concentration and temperature, on the recovery degree of
zinc and copper from aqueos solutions.
Experimental part
In order to achieve a good chemical analysis we used:
chemical reagents such as Merck, Fluka: CuSO4 . 5H2O,
ZnSO4 . 7H2O and standard sample solutions of 1000 mg
Zn/L and 1000 mg Cu/L, bidistilled water, volumetric
solutions of: oxalic acid 0.5M, with factor 1.00; potassium
permanganate 0.1N; nitric acid 1N; hydrochloric acid 18%,
sulfuric acid 4N; disodic salt of the ethylene diamine
tetraacetic acid 0.05 M (complexon III), ammonia buffer
solution (pH=10), metal-chromic indicators: eriochrome
black T and murexide, 10% biammoniacal phosphate
solution. The copper and zinc content from the analysed
solutions were determined by complexonometric,
gravimetric and spectrometry methods [11-13].
The apparatus used was: digital pH-meter, electric
thermostatic drying system, Electrolyser-Germany, flame
atomic absorption spectophotometer AAS-30 (FAAS), 1500
D MOM – Budapest derivatograph.
Synthetic solutions of CuSO4 and ZnSO4 of different
concentrations were prepared and treated with 0.5M oxalic
acid in well established ratios, at a certain temperature
and pH, under continous stirring. The obtained precipitates
were settled, filtered, washed, dried and analyzed. A well
determined quantity of the obtained product was dissolved
in 18% hydrochloric acid. The obtained solutions were
passed into 100 mL flasks, taking appropriate samples for
the analysis of the zinc and copper content.
The analysis of zinc and copper cations was achieved
by the gravimetric method (as zinc pirophosphate),
electrogravimetric (copper), complexonometric with EDTA
(in presence of eriochrome black T for Zn2+ and murexide
indicator for Cu 2+ ) and by flame atomic adsorption
spectrofotometry (FAAS) according to SR ISO 8288. The
oxalate anion was analyzed by permanganometric titration.
The thermal studies were achieved under the following
conditions: the analysed mass sample: 100 mg, heating
rate 5°C/minute, temperature range 0-500°C, platinum
crucible, inert material: α -Al2O3, in static air atmosphere
[14].
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Results and discussions
The precipitation of zinc and copper, as zinc oxalate
and copper oxalate, is based on the following reaction
equations:
Zn2+ + C2 O42- + 2H2O = Zn C2 O4 · 2H2O ↓ crystalline white (1)
Cu2+ + C2 O42- + 0.5H2O= CuC2 O4 · 0,5H2O ↓ light green
(2)
The recovery yield of the cation has been calculated
using the following formula:
(3)
where:
-α = recovery degree, %
-Ci,Me2+ = concentration of the cation in [mg/L] before
the precipitation with oxalic acid
-Cf,Me2+ = concentration of the cation in [mg/L] after the
precipitation as an oxalate.
There has been monitored the influence of various
parameters, such as: reaction mass pH, dose of
precipitation reagent, concentration and temperature, on
the recovery degree of zinc and copper from the studied
solutions.
Reaction mass pH
The experimental data regarding the reaction mass pH
influence on the recovery degree of zinc and copper
oxalates (FAAS analysis) from 0.1M Zn2+ and 0.1M Cu2+
sulphates solutions, at 20°C, with a reaction time of 10
min, mechanical stirring at 300 rpm and a reagent excess
Fig. 2. Dependence recovery yield of metalic oxalates- oxalic acid
excess
Based on the experimental data, the optimum pH value
for a maximum recovery degree of zinc and copper ions
as oxalates is framed in the range 4.5-5.5 for both cations.
Dose of oxalic acid
The experimental data obtained from the oxalates
precipitation at 20 oC, pH=5.5, reaction time 10 min,
mechanically stirred at 300 rpm, regarding the influence
of exceeding oxalic acid on the recovery degree is shown
in figure 2.
The remaining metallic ion concentration (Zn+2 and Cu+2,
respectively) for various values of the precipitating reagent
excess was confirmed by FAAS and complexonometric
titrimetry.
The curves presented in figure 2, show that the copper
and zinc ion recovery degree as crystalline oxalates
increases with precipitating reagent excess.
The study of optimizing α parameter, in terms of oxalic
acid excess, shows that for an oxalic acid excess of 10%,
the recovery process of zinc and copper ions is ~97%. The
further increase of oxalic acid excess up to ~60% leads to
an improvement of the recovery degree with 1.8% for
copper and 1.0% for zinc. These data show that it is
necessary to use an optimum excess of oxalic acid up to
60 % in order to obtain a maximum recovery degree:
around 99% for zinc ion and 98% for copper ion.
The influence of the initial cation concentration
There has been monitored the influence of the initial
zinc cation, as zinc oxalate concentration at 20oC on the
recovery degree. The experimental data obtained at
optimum pH, optimum oxalic acid dose, reaction time 10
Fig.1. Dependence recovery yield of metalic oxalatesreaction mass pH at 20oC
of 10% oxalic acid, are shown in figure 1. The H2SO4 and
10% NaOH solutions were used as pH correction agents.
The experimental data revealed that the recovery degree
of zinc and copper oxalates is influenced by the pH of the
reaction mass: the increase of the pH in the studied pH
range determines a higher recovery degree. The increase
of parameter α in the pH range 1-5 is 22.4% in case of Cu2+
recovery (significant increase in the pH range 3 -5)
compared to the lower increase of only 2.4% in case of
Zn2+ recovery. The recovery degree of the zinc cation is
less influenced by the pH increase, achieving values higher
than 95% in the studied pH range. For pH=5, the recovery
degree of the zinc cation was 97.7%.
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Fig. 3. Dependence recovery yield of zinc oxalate- zinc
concentration at 20oC
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Fig. 4. Dependence recovery yield of
metalic oxalates- initial
concentration of metalic ions
at 70-80oC
The chemical composition of copper and zinc oxalates
The copper and zinc oxalates that have been obtained
in optimum conditions, in form of crystalline precipitates,
were filtered, washed, dried and subdued to a chemical
Table 1
CHEMICAL COMPOSITION OF ZINC OXALATE
Table 2
CHEMICAL COMPOSITION OF COPPER OXALATE
gravimetric analysis (for the cations) and from the
permanganometric analysis (for the oxalate anion) are
shown in table 1 and 2.
The gravimetric and complexonometric analysis of the
zinc and copper content from the solutions 1 and 2, in form
of zinc and copper pyrophosphate, confirm the metal
percentage from the studied oxalates: 34.5% Zn and 39.6%
Cu.
The experimental results confirm the form of dihydrated
zinc oxalate: ZnC 2O4·2H 2O and semi-hydrated copper
oxalate: CuC2O4·0.5H2O.
Temp.[oC]
d.)The temperature influence
The results of the research regarding the temperature
influence, at 70-80oC, on the recovery degree for various
cation concentrations are shown in figure 4. The remaining
zinc and copper content has been complexonometrically
determined, the results being close to the ones obtained
by FAAS.
Figure 4 reveals that in case of the zinc cation, in the
concentration range (0.01-0.033M), the recovery degree
increases with temperature increase from 20°C to 70°C
(2%), while at concentrations of C ≥ 0.033M, the
temperature influence is insignificant. In case of the copper
ion was noticed a similar temperature influence on the
recovery degree.
The graphic shows that the temperature influences,
significantly, the recovery degree of the copper cation. The
recovery efficiency of copper increases from 83% to 98.9%,
in the concentration range 0.01-0.05M, while for
concentrations of [C] ≥ 0.055M, the temperature is
insignificant for the copper recovery degree, α having a
maximum value of 98.9%.
From the presented ones we can consider as optimum
process temperature: T= 20°C, for the zinc cation and
T = 700 C, for the copper cation.
analysis according to chapter 2, in order to obtain the
chemical formula and the chemical composition of the
extracted compounds.
The experimental data on the chemical composition of
the oxalates obtained from complexonometric and
Fig. 5. Derivatogram of
the obtained zinc
oxalate
Loss[%]
min and mechanically stirring at 300 rpm, are shown in
figure 3. The remaining cation concentration
determinations by complexonometric analysis were close
to the ones obtained by FAAS.
The experimental data regarding the influence of the
zinc cation concentration on the recovery degree value at
20oC, showed that, the recuperative purging process in form
of zinc oxalate runs well for 0.1M, which holds the
maximum efficiency value of 98.7%. For the studied
minimum zinc concentration (0.01M), the recovery degree
is 91.2%.
The purging process is positively influenced by the
increase of the zinc cation concentration. Between 0.010.1M, α parameter tends to reach a constant value, 96.9%,
for a concentration, [C] ≥ 0.033M. For concentrations of
zinc ion, [C] ≥ 0.05M, α parameter is achieving 99%
efficiency, in form of crystallized zinc oxalate.
From the technical point of view, this is considered an
efficient process of wastewater zinc recovery.
Time
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Temp.[oC]
Loss[%]
Fig. 6. Derivatogram of the obtained
copper oxalate
Time
Table 3
THERMAL ANALYSIS RESULTS OF ZINC AND COPPER OXALATE
Table 4
OPTIMUM RECOVERY CONDITIONS OF ZINC AND COPPER OXALATE
Thermal analysis
The derivatograms for zinc oxalate and copper oxalate,
respectively, are presented in figure 5 and figure 6.
The thermal decomposition of the oxalates results from
the following equations:
ZnC2O4.2H2O→ZnC2O4+2H2O
ZnC2O4 ¯ ³→ ZnO + CO2 + CO
CuC2O4· 0,5H2O → CuC2O4 +1/2 H2O
CuC2O4 → CuO + CO2 + CO
(4)
(5)
(6)
(7)
The experimental data obtained from thermal analysis
are presented in table 3.
The results confirm that the zinc and copper oxalates
precipitate as ZnC2O4·2H2O and CuC2O4·0.5H2O, confirming
the determined chemical composition.
Conclusions
The optimal conditions for the precipitation of zinc and
copper as dihydrated zinc oxalate and semi-hydrated
copper oxalate, established from the achieved studies, are
presented in table 4.
Zinc and copper precipitation with 99% yield in the
optimal conditions, ascertains the preparation of insoluble
crystalline precipitate of dihydrated zinc oxalate and
semihydrated copper oxalate. These cr ystalline
precipitates are stable in air, carbon dioxide and light, unlike
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the known amorphic forms of the hydroxides, carbonates,
basic carbonates.
The precipitation of zinc and copper ions as oxalates,
using the method presented in the paper, can be used for
cleaning of residual solutions derived from coppering of
carbon brushes and acid zinc coating on metal sheet from
S.C.Electroargeº Curtea de Argeº (under consideration).
The purging process of zinc and copper ions as oxalates,
from various residual effluents has the following
advantages:
- speed of cleaning, filtering, washing- superior to the
amorphic forms;
- low and compact volume of the precipitate;
- low energy costs for by-products with various usage:
zinc oxide and copper oxide;
- the transformation of zinc and copper oxalates, initially
obtained, into zinc and copper salts;
- a precipitation reagent that is economically accesible
(synthesis, price, transport, chemical stability);
- the optimum pH values are easy to obtain using suitable
substances, also dose of oxalic acid and the temperatute
if it necessary;
- the crystalline oxalates can be easyly transformed in
pure oxides, at low temperature, about 3500C, or using
subsequant application.
The oxalic acid excess and the remaining cation can be
eliminated by treating the filtered product and scouring
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waters with 10% milk of lime. Thus, the oxalate anion is
varved as calcium oxalate and the remaining cation
precipitates as a hydroxide, the pH of the solution is
corrected, the metal (zinc or copper) content being under
0.1mg/L, and the effluent can be disposed according to
the enviromnent and waters quality legislation.
The recover y as metal oxalates resolves the
environmental problems as well as the recovery of
transitional metals [7-10].
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Manuscript received: 14.10.2008
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