RESULTS AND DISCUSSION
5.1 Metal ions availability in aqueous phase with variation in solution pH from mono-, binary- and ternary-metal ion systems comprising of Cu(II), Pb(II) and
Cr(III) ions
The metal availability in aqueous phase from mono-, binary- and ternary-metal ion systems comprising of Cu(II), Pb(II) and Cr(III) metal ions was investigated with variation in solution pH. The results of these studies shall be useful to understand the role of solution pH on metal removal from the aqueous phase either by precipitation or adsorption or by both the processes.
5.1.1 Availability of metal ions in aqueous phase with variation in solution pH from mono- metal ion systems comprising of Cu(II), Pb(II) and Cr(III) ions
The experiments were conducted for mono-metal ion systems of M[Cu(0.60)], M[Pb(0.60)] and M[Cr(0.60)] and solution pH was varied from 5.00 to 7.00. This pH range was selected based on the desired initial pH of the solution and final pH observed during the course of a few preliminary tests. The variation in trend of availability of metal ions in aqueous phase from M[Cu(0.60)], M[Pb(0.60)] and M[Cr(0.60)] systems is represented in Fig. 5.1. In the case of M[Cu(0.60)] system, Cu(II) metal ion was available 100% in aqueous phase up to solution pH 5.50 while its availability reduced to approximately 95% at pH 6.00, 28% at pH 6.50 and 5% at pH 7.00. The availability of Cu(II) in aqueous phase decreased rapidly between pH 6.00 and 7.00. The theoretically calculated Cu(II) availability in aqueous phase at solution pH 6.00 was 97% (Christophi & Axe, 2000). In the case of M[Pb(0.60)]
system, Pb(II) metal ion was available approximately 100% in aqueous phase up to pH 5.50 which reduced to approximately 72% at pH 6.00, 6% at pH 6.50 and 2% at pH 7.00. The availability of Pb(II) in aqueous phase also decreased rapidly between pH 6.00 and 7.00. The theoretically calculated Pb(II) availability in aqueous phase at solution pH 6.00 was 96.4%
which was much higher to experimentally observed availability (Christophi & Axe, 2000). In the case of M[Cr(0.60)] system, Cr(III) metal ion was available close to 100% in aqueous phase up to pH 6.00 which reduced to 84% at pH 6.50 and 63% at pH 7.00. Therefore, Cu(II) and Cr(III) may be considered 100% available in aqueous phase up to pH value of 6.00, while availability of Pb(II) in aqueous phase may be considered 72% up to pH value of 6.00. Since
Fig. 5.1: Availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase with variation in solution pH from respective mono-metal ion systems {Initial metal conc. in M[Cu(0.60)] = 0.60±0.00 meq/L, M[Pb(0.60)] = 0.60±0.00 meq/L, M[Cr(0.60)] = 0.60±0.00 meq/L, Temp. = 30±2°C} (Each data represents an average of two independent experimental values with vertical bars representing 95% confidence interval).
availability in aqueous phase of close to or more than 70% of Pb(II) and more than 80% of Cu(II) and Cr(III) metal ions are up to pH of 6.00, and hence the same has been considered in the study.
5.1.2 Availability of metal ions in aqueous phase with variation in solution pH from binary- metal ion systems comprising of Cu(II), Pb(II) and Cr(III) ions
The experiments were conducted for binary-metal ion systems comprising of Cu(II)+Pb(II), Cr(III)+Pb(II) and Cu(II)+Cr(III) metal ions with four different combinations of initial metal ion concentrations as described in section 4.2.1 (Table 4.5). The solution pH was varied in the range of 5.00 to 7.00. This pH range was selected based on the desired initial pH of the solution and final pH observed during the course of a few preliminary tests.
The percentage of metal ions remaining in aqueous phase estimated at each pH for different combinations of binary-metal ion systems comprising of Cu(II)+Pb(II) is presented in Fig.
5.2. Both the metal ions were 100% available in aqueous phase at pH 5.00 in B[Cu(0.45)+Pb(0.15)], B[Cu(0.30)+Pb(0.30)], B[Cu(0.15)+Pb(0.45)] and B[Cu(0.60)+Pb(0.60)] combinations. The Cu(II) metal ions availability in aqueous phase reduced approximately to 95%, 93%, 96% and 88% in B[Cu(0.45)+Pb(0.15)], B[Cu(0.30)+Pb(0.30)], B[Cu(0.15)+Pb(0.45)] and B[Cu(0.60)+Pb(0.60)] combinations respectively at solution pH 5.50. The availability of Pb(II) metal ions in aqueous phase were
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in M[Cu(0.60)]
Pb(II) in M[Pb(0.60)]
Cr(III) in M[Cr(0.60)]
Fig. 5.2: Availability of Cu(II) and Pb(II) metal ions in aqueous phase with variation in solution pH from binary-metal ion system combinations (a) B[Cu(0.45)+Pb(0.15)], (b) B[Cu(0.30)+Pb(0.30)], (c) B[Cu(0.15)+Pb(0.45)] and (d) B[Cu(0.60)+Pb(0.60)] {Initial metal conc. in combinations B[Cu(0.45)+Pb(0.15)] = 0.44±0.00 meq/L of Cu(II) + 0.15±0.00 meq/L of Pb(II), B[Cu(0.30)+Pb(0.30)] = 0.30±0.00 meq/L of Cu(II) + 0.29±0.00 meq/L of Pb(II), B[Cu(0.15)+Pb(0.45)] = 0.15±0.00 meq/L of Cu(II) + 0.45±0.00 meq/L of Pb(II), B[Cu(0.60)+Pb(0.60)] = 0.61±0.00 meq/L of Cu(II) + 0.58±0.01 meq/L of Pb(II)} (Each data represents an average of two independent experimental values with vertical bars at each data points representing 95% confidence interval).
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availabilit
(a) pH
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availability
(b) pH
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in B[Cu(0.15)+Pb(0.45)]
Pb(II) in B[Cu(0.15)+Pb(0.45)]
(c)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in B[Cu(0.60)+Pb(0.60)]
Pb(II) in B[Cu(0.60)+Pb(0.60)]
(d)
observed approximately to 99%, 97%, 95% and 95% in B[Cu(0.45)+Pb(0.15)], B[Cu(0.30)+Pb(0.30)], B[Cu(0.15)+Pb(0.45)] and B[Cu(0.60)+Pb(0.60)] combinations respectively at solution pH 5.50. At solution pH 6.00, Cu(II) availability in aqueous phase reduced approximately to 90%, 89%, 80% and 80% while Pb(II) availability in aqueous phase reduced approximately to 96%, 91%, 89% and 88% in B[Cu(0.45)+Pb(0.15)], B[Cu(0.30)+Pb(0.30)], B[Cu(0.15)+Pb(0.45)] and B[Cu(0.60)+Pb(0.60)] combinations respectively. Further, the availability of Cu(II) and Pb(II) in aqueous phase decreased rapidly between pH 6.00 and 7.00. The Cu(II) metal ion availability in aqueous phase at pH 7.00 reduced to 8%, 13%, 49% and 5% while for Pb(II) metal ion, it reduced to 23%, 10%, 17%
and 8% respectively in B[Cu(0.45)+Pb(0.15)], B[Cu(0.30)+Pb(0.30)], B[Cu(0.15)+Pb(0.45)]
and B[Cu(0.60)+Pb(0.60)] combinations. Therefore, availability in aqueous phase of close to or more than 80% of Cu(II) and Pb(II) metal ions were up to solution pH of 6.00 and has been considered accordingly in the present study.
The variation in trend of availability of metal ions in aqueous phase from four different combinations of binary-metal ion systems comprising of Cr(III)+Pb(II) is represented in Fig. 5.3. Both the metal ions were 100% available in aqueous phase till pH 5.00 in B[Cr(0.45)+Pb(0.15)], B[Cr(0.30)+Pb(0.30)], B[Cr(0.15)+Pb(0.45)] and B[Cr(0.60)+Pb(0.60)] combinations. The Cr(III) metal ions availability in aqueous phase were observed approximately 99%, 97%, 91% and 99% respectively in B[Cr(0.45)+Pb(0.15)], B[Cr(0.30)+Pb(0.30)], B[Cr(0.15)+Pb(0.45)] and B[Cr(0.60)+Pb(0.60)] combinations at solution pH 5.50. The Pb(II) metal ions availability in aqueous phase at pH 5.50 were observed approximately 94%, 100%, 95% and 96%
respectively in B[Cr(0.45)+Pb(0.15)], B[Cr(0.30)+Pb(0.30)], B[Cr(0.15)+Pb(0.45)] and B[Cr(0.60)+Pb(0.60)] combinations. At pH 6.00, Cr(III) availability in aqueous phase reduced approximately to 95%, 73%, 60% and 85% while Pb(II) availability in aqueous phase were reduced approximately to 87%, 83%, 88% and 85% respectively in B[Cr(0.45)+Pb(0.15)], B[Cr(0.30)+Pb(0.30)], B[Cr(0.15)+Pb(0.45)] and B[Cr(0.60)+Pb(0.60)] combinations. Further, the availability of Cr(III) and Pb(II) in aqueous phase decreased rapidly between pH 6.00 and 7.00. Therefore, availability of more than 80%
of Cr(III) and Pb(II) metal ions in aqueous phase were up to solution pH of 6.00 except for Cr(III) metal ions in B[Cr(0.30)+Pb(0.30)] and B[Cr(0.15)+Pb(0.45)] combinations.
Fig. 5.3: Availability of Cr(III) and Pb(II) metal ions in aqueous phase with variation in solution pH from binary-metal ion system combinations (a) B[Cr(0.45)+Pb(0.15)], (b) B[Cr(0.30)+Pb(0.30)], (c) B[Cr(0.15)+Pb(0.45)] and (d) B[Cr(0.60)+Pb(0.60)] {Initial metal conc. in combinations B[Cr(0.45)+Pb(0.15)] = 0.41±0.00 meq/L of Cr(III) + 0.15±0.00 meq/L of Pb(II), B[Cr(0.30)+Pb(0.30)] = 0.29±0.00 meq/L of Cr(III) + 0.30±0.00 meq/L of Pb(II), B[Cr(0.15)+Pb(0.45)] = 0.15±0.00 meq/L of Cr(III) + 0.45±0.00 meq/L of Pb(II), B[Cr(0.60)+Pb(0.60)] = 0.58±0.00 meq/L of Cr(III) + 0.60±0.00 meq/L of Pb(II)} (Each data represents an average of two independent experimental values with vertical bars at each data points representing 95% confidence interval).
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availability
(a) pH
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availability
(b) pH
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Pb(II) in B[Cr(0.15)+Pb(0.45)]
Cr(III) in B[Cr(0.15)+Pb(0.45)]
(c)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Pb(II) in B[Cr(0.60)+Pb(0.60)]
Cr(III) in B[Cr(0.60)+Pb(0.60)]
(d)
The metal ions availability in aqueous phase from four different combinations of binary-metal ion systems comprising of Cu(II)+Cr(III) were also investigated with variation in solution pH and results are shown in Fig. 5.4. The study revealed precipitation of Cu(II) and Cr(III) metal ions at pH 5.00 in B[Cu(0.30)+Cr(0.30)], B[Cu(0.45)+Cr(0.15)] and B[Cu(0.60)+Cr(0.60)] combinations except in B[Cu(0.15)+Cr(0.45)] combination. At pH 5.00, Cu(II) metal ions availability in aqueous phase reduced to 48%, 29% and 11%
respectively in B[Cu(0.45)+Cr(0.15)], B[Cu(0.30)+Cr(0.30)] and B[Cu(0.60)+Cr(0.60)]
combinations while it was available in aqueous phase up to 98% in B[Cu(0.15)+Cr(0.45)]
combination. Similarly for Cr(III) metal ion, the availability in aqueous phase at pH 5.00 reduced to 1%, 40% and 33% respectively in B[Cu(0.45)+Cr(0.15)], B[Cu(0.30)+Cr(0.30)]
and B[Cu(0.60)+Cr(0.60)] combinations while it was available in aqueous phase up onto 97%
in B[Cu(0.15)+Cr(0.45)] combination. These observations indicated that the presence of Cu(II) and Cr(III) metal ions together in the solution has had profound effect on their availability in aqueous phase around solution pH of 5.00.
5.1.3 Availability of metal ions in aqueous phase with variation in solution pH from ternary-metal ion system comprising of Cu(II), Pb(II) and Cr(III) ions
The Cu(II), Pb(II) and Cr(III) metal ions availability in aqueous phase were also investigated from two different combinations of ternary-metal ion systems viz.
T[Cu(0.20)+Pb(0.20)+Cr(0.20)] and T[Cu(0.60)+Pb(0.60)+Cr(0.60)]. Fig. 5.5 depicts availability of metal ions in aqueous phase with variation in solution pH. At pH 5.00, the availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase were observed approximately 100%, 97% and 98% respectively in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
combination, which further reduced approximately to 17%, 82% and 10% respectively at solution pH 5.50. It indicated substantial precipitation of Cu(II) and Cr(III) metal ions compared to Pb(II) metal ions when these metals were present together in solution. In the case of T[Cu(0.60)+Pb(0.60)+Cr(0.60)] combination, the availability of Cu(II) and Cr(III) metal ions in aqueous phase at solution pH 5.00 reduced approximately to 17% and 37%
respectively compared to Pb(II) metal ions which was 99%. Further, the availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase reduced approximately to 2%, 82% and 5% respectively at pH 5.50. In this combination also, the observed precipitation of Cu(II) and Cr(III) metal ions were higher compared to Pb(II) metal ions. The inclusion of Cu(II) in ternary-metal ion system of Cu(II)+Pb(II)+Cr(III) (Fig. 5.5) has had marked effect on availability of all the metal ions in aqueous phase at solution pH of 5.00 or more.
Fig. 5.4: Availability of Cu(II) and Cr(III) metal ions in aqueous phase with variation in solution pH from binary-metal ion system combinations (a) B[Cu(0.45)+Cr(0.15)], (b) B[Cu(0.30)+Cr(0.30)], (c) B[Cu(0.15)+Cr(0.45)] and (d) B[Cu(0.60)+Cr(0.60)] {Initial metal conc. in combinations B[Cu(0.45)+Cr(0.15)] = 0.44±0.00 meq/L of Cu(II) + 0.16±0.00 meq/L of Cr(III), B[Cu(0.30)+Cr(0.30)] = 0.30±0.00 meq/L of Cu(II) + 0.27±0.00 meq/L of Cr(III), B[Cu(0.15)+Cr(0.45)] = 0.15±0.00 meq/L of Cu(II) + 0.41±0.00 meq/L of Cr(III), B[Cu(0.60)+Cr(0.60)] = 0.60±0.00 meq/L of Cu(II) + 0.59±0.01 meq/L of Cr(III)} (Each data represents an average of two independent experimental values with vertical bars at each data points representing 95% confidence interval).
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availabili
(a) pH
0 20 40 60 80
5.00 5.50 6.00 6.50 7.00
Metal availability
(b) pH
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in B[Cu(0.15)+Cr(0.45)]
Cr(III) in B[Cu(0.15)+Cr(0.45)]
(c)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in B[Cu(0.60)+Cr(0.60)]
Cr(III) in B[Cu(0.60)+Cr(0.60)]
(d)
Fig. 5.5: Availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase with variation in solution pH from ternary-metal ion system combinations (a) T[Cu(0.20)+Pb(0.20)+Cr(0.20)] and (b) T[Cu(0.60)+Pb(0.60)+Cr(0.60)] {Initial metal conc. in combinations T[Cu(0.20)+Pb(0.20)+Cr(0.20)] = 0.20±0.00 meq/L of Cu(II) + 0.21±0.00 meq/L of Pb(II) + 0.20±0.00 meq/L of Cr(III);
T[Cu(0.60)+Pb(0.60)+Cr(0.60)] = 0.60±0.00 meq/L of Cu(II) + 0.59±0.00 meq/L of Pb(II) + 0.60±0.00 meq/L of Cr(III)} (Each data represents an average of two independent experimental values with vertical bars representing 95% confidence interval).
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
Pb(II) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
Cr(III) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
(a)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
Pb(II) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
Cr(III) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
(b)
The speciation of metal ions in all the combinations of mono-, binary- and ternary metal ion systems comprising of Cu(II), Pb(II) and Cr(III) were also investigated under uncontrolled and controlled pH conditions using MINEQL+ software (Schecher & McAvoy, 1998). The input parameters such as initial concentrations of different components [viz., Cu(II), Pb(II), Cr(III), SO42-, NO3-, CH3COO-, Na+, etc.] present in aqueous phase were estimated based on the initial experimental conditions adopted in section 4.3. The speciation of metal ions under uncontrolled pH conditions was estimated for pH range of 5.00 to 7.00.
All the concentrations of metal species present in ionic form were added together to estimate the percentage of metal availability in the aqueous phase.
The availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase from mono-, binary- and ternary-metal ion systems with variation in solution pH are shown in Fig. 5.6 to 5.8. The estimated availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase from mono-metal ions systems at solution pH 5.50 were approximately 98%, 98% and 21%
respectively. The estimated availability of Cr(III) metal ion in aqueous phase was much lower than the approximately 100% availability estimated experimentally as presented in section 5.1.1. The estimated availability of metal ions in aqueous phase from combinations of binary- metal ion systems indicated much higher reduction beyond pH 5.50 for Cu(II)+Pb(II) and
Fig. 5.6: Availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase with variation in solution pH estimated using MINEQL+ software from mono-metal
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in M[Cu(0.60)]
Pb(II) in M[Pb(0.60)]
Cr(III) in M[Cr(0.60)]
Fig. 5.7: Availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase with variation in solution pH estimated using MINEQL+ software from combinations of binary-metal ion systems.
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Cu(II) in B[Cu(0.45)+Pb(0.15)]
Pb(II) in B[Cu(0.45)+Pb(0.15)]
Metal availability (%)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Cu(II) in B[Cu(0.30)+Pb(0.30)]
Pb(II) in B[Cu(0.30)+Pb(0.30)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Cu(II) in B[Cu(0.15)+Pb(0.45)]
Pb(II) in B[Cu(0.15)+Pb(0.45)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Cu(II) in B[Cu(0.60)+Pb(0.60)]
Pb(II) in B[Cu(0.60)+Pb(0.60)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Pb(II) in B[Cr(0.45)+Pb(0.15)]
Cr(III) in B[Cr(0.45)+Pb(0.15)]
Metal availability (%)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Pb(II) in B[Cr(0.30)+Pb(0.30)]
Cr(III) in B[Cr(0.30)+Pb(0.30)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Pb(II) in B[Cr(0.15)+Pb(0.45)]
Cr(III) in B[Cr(0.15)+Pb(0.45)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00 Pb(II) in B[Cr(0.60)+Pb(0.60)]
Cr(III) in B[Cr(0.60)+Pb(0.60)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
pH
Cu(II) in B[Cu(0.45)+Cr(0.15)]
Cr(III) in B[Cu(0.45)+Cr(0.15)]
Metal availability (%)
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
pH
Cu(II) in B[Cu(0.30)+Cr(0.30)]
Cr(III) in B[Cu(0.30)+Cr(0.30)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
pH
Cu(II) in B[Cu(0.15)+Cr(0.45)]
Cr(III) in B[Cu(0.15)+Cr(0.45)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
pH
Cu(II) in B[Cu(0.60)+Cr(0.60)]
Cr(III) in B[Cu(0.60)+Cr(0.60)]
Fig. 5.8: Availability of Cu(II), Pb(II) and Cr(III) metal ions in aqueous phase with variation in solution pH estimated using MINEQL+ software from combinations of ternary-metal ion systems.
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
Pb(II) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
Cr(III) in T[Cu(0.20)+Pb(0.20)+Cr(0.20)]
0 20 40 60 80 100 120
5.00 5.50 6.00 6.50 7.00
Metal availability (%)
pH
Cu(II) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
Pb(II) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
Cr(III) in T[Cu(0.60)+Pb(0.60)+Cr(0.60)]
Pb(II)+Cr(III) combinations and beyond pH 5.00 for Cu(II)+Cr(III) combinations. These observations were not in consonance with the experimentally observed reduction in metal availability in aqueous phase. Similarly, the estimated metal availability in aqueous phase was much off the track compared to experimental results obtained for ternary-metal ion systems.
The solution pH was fixed at 5.00 under controlled pH conditions and hence the availability of different species of metal ions was estimated at pH 5.00 using MINEQL+
software. The results are presented in Table 5.1. It appeared that more than 80% of Cu(II), Pb(II) and Cr(III) metal ions were available in aqueous phase in the form of metal-acetate complex.
5.1.5 Summary
The availability of metal ions in aqueous phase with variation in solution pH from mono-, binary- and ternary-metal ion systems was experimentally investigated. The availability of Cu(II) and Cr(III) metal ions in aqueous phase from mono-metal ion system was ≥ 80% up to solution pH 6.00, while for Pb(II) metal ion it was ≥ 70%. Similarly the availability of ≥ 80% of metal ions in aqueous phase were observed up to solution pH of 6.00 from all the four combinations of binary-metal ion systems of Cu(II)+Pb(II), Cr(III)+Pb(II) except Cr(III) metal ions availability in B[Cr(0.30)+Pb(0.30)] and B[Cr(0.15)+Pb(0.45)]
combinations which was ≤ 73%. However metal availability in aqueous phase drastically reduced in all four combinations of Cu(II)+Cr(III) and two combinations of ternary-metal ion systems even at solution pH of 5.00 or higher due to precipitation or co-precipitation of metal ions. The metal availability in aqueous phase at different solution pH estimated using MINEQL+ software were not in agreement with the experimental results obtained. The metal availability in aqueous phase at controlled pH 5.00 from mono-, binary- and ternary-metal ion systems using MINEQL+ software estimated more than 80% for Cu(II), Pb(II) and Cr(III) metal ions in the form of metal-acetate complex. The results of these investigations are likely to help in understanding metal removal from aqueous phase during subsequent investigations.
Table 5.1: Speciation of Cu(II), Pb(II) and Cr(III) metal ions from mono-, binary- and ternary-metal ions systems under controlled pH conditions.
Metal ion systems
Metal ion combinations
Cu speciation (%) Pb speciation (%) Cr speciation (%)
Cu2+ Cu(CH3COO)3- Cu(CH3COO)+ Cu(CH3COO)2 Pb2+ Pb(CH3COO)2 Pb(CH3COO)+ Cr(CH3COO)3 Cr(CH3COO)2+
Mono
M[Cu(0.60)] 10.9 2.1 45.2 41.2 - - - - -
M[Pb(0.60)] - - - - 3.4 35.8 60.1 - -
M[Cr(0.60)] - - - - - - - 91.8 7.2
Binary
B[Cu(0.45)+Pb(0.15)] 8.9 2.2 44.8 43.9 2.7 37.9 58.9 - -
B[Cu(0.30)+Pb(0.30)] 8.9 2.2 44.8 44.0 2.7 38.0 58.5 - -
B[Cu(0.15)+Pb(0.45)] 8.9 2.2 44.8 44.0 2.7 38.0 58.5 - -
B[Cu(0.60)+Pb(0.60)] 9.2 2.1 45.1 43.3 2.8 37.4 58.9 - -
B[Cr(0.45)+Pb(0.15)] - - - - 2.8 37.2 59.3 91.9 7.2
B[Cr(0.30)+Pb(0.30)] - - - - 2.8 37.5 59.0 92.0 7.1
B[Cr(0.15)+Pb(0.45)] - - - - 2.8 37.7 58.8 92.1 7.0
B[Cr(0.60)+Pb(0.60)] - - - - 3.0 36.4 60.0 91.6 7.4
B[Cu(0.45)+Cr(0.15)] 9.0 2.1 45.0 43.7 - - - 92.1 7.0
B[Cu(0.30)+Cr(0.30)] 9.2 2.1 45.2 43.4 - - - 92.0 7.1
B[Cu(0.15)+Cr(0.45)] 9.3 2.0 45.5 43.1 - - - 91.9 7.2
B[Cu(0.60)+Cr(0.60)] 9.8 1.9 46.0 42 - - - 91.5 7.4
Ternary T[Cu(0.20)+Pb(0.20)+Cr(0.20)] 9.1 2.1 45.1 43.6 2.8 37.6 58.9 92.0 7.1
T[Cu(0.60)+Pb(0.60)+Cr(0.60)] 10.0 1.9 46.3 41.5 3.1 35.7 60.4 91.4 7.6
81
5.2 Effect of contact time on metal ion concentration remaining in aqueous phase