Turbidity Removal by Polyelectrolytes as Flocculant Aids
303
overdose at aluminium nitrate concentrations up to 10- 2 M. This is typical in the
case of sweeping mechanism (Hyaden and Rubin 1974; Rubin and Bocksidge
1979; Dentel and Gossett 1988) by the positively charged semiprecipitated
aluminium hydroxides.
3.2 Cationic Polyelectrolytes as Primary Flocculants
Figures 2 and 3 show the turbidity removal and the electrophoretic mobility curves
of the clay mineral suspension flocculated with cationic polyelectrolytes. The
curves show typical behaviour for polymeric flocculation (Rebhun 1966; Rebhun
et al. 1968; Narkis 1968; Narkis and Rebhun 1975). In all polymer flocculation
curves, the underdose, good clarification and overdose regions appear. The
optimum flocculation was always achieved with almost no change in the original
electrophoretic mobility. The most significant change in the EM at the optimal
flocculant dose was noticed with Separan Cp-400, which is a copolymer of
acrylamide and cationic quaternary polyamine, with the lowest charge density.
Therefore, it is the less cationic among the polymers, used as shown in Fig. 3. The
zero EM was obtained with all polymers either at the end of the good clarification,
or at the beginning of the overdose range. The effect of the polymer charge
density was noticed only in the copolymers' case. The Separan Cp-402, which has
a higher charge density than Separan Cp-400, was more effective despite its lower
molecular weight. In the range of the charge densities examined, the differences in
the polyamine charge densities had no systematic influence on the polymers'
optimal dose, or on their corresponding electrophoretic mobilities, as shown in
Fig. 2. The differences noticed between the polyamines and the copolymers with
polyacrylamide in the flocculation curves are as follows:
• The optimal flocculant dose (OFD) of the copolymers was noticeably higher
than that of the polyamines. The optimal dose of Separan Cp-400 was 5.0 £-1 as
compared to 0.6 - 0.8 mg £-1 of the polyamines and 12 mg £-1 of the nonionic polyacrylamide Magnifloc MG202 (Narkis et al. 1990).
• A greater change in EM was obtained with the copolymers than with
.
-1 -1
-1
-1 -1
-1
homopolyammes. EM values of -0.6 /l s V cm and -1.6 /l s V cm were
obtained at the optimal dose for Separan Cp-400 and Cp-402, respectively, as for
the homopolyamines, while no significant change in the EM was noticed at the
optimal flocculant dose.
• The asymptotic values of the EM in the charge reversal region was greater with
the cationic copolymers, particularly with Cp-402, where an asymptotic EM
-1
-f
-1
value of more than +5.0 /l s V cm was obtained. Similar results were
reported by Shun and Gregory (1990).
• In some of the polyarnines' flocculation curves, the turbidity increases steeply
in the overdose range, whereas with the copolymer Separan Cp-402, the turbidity
increases gradually, and with Separan Cp-400 almost no overdose is noticed up
303
overdose at aluminium nitrate concentrations up to 10- 2 M. This is typical in the
case of sweeping mechanism (Hyaden and Rubin 1974; Rubin and Bocksidge
1979; Dentel and Gossett 1988) by the positively charged semiprecipitated
aluminium hydroxides.
3.2 Cationic Polyelectrolytes as Primary Flocculants
Figures 2 and 3 show the turbidity removal and the electrophoretic mobility curves
of the clay mineral suspension flocculated with cationic polyelectrolytes. The
curves show typical behaviour for polymeric flocculation (Rebhun 1966; Rebhun
et al. 1968; Narkis 1968; Narkis and Rebhun 1975). In all polymer flocculation
curves, the underdose, good clarification and overdose regions appear. The
optimum flocculation was always achieved with almost no change in the original
electrophoretic mobility. The most significant change in the EM at the optimal
flocculant dose was noticed with Separan Cp-400, which is a copolymer of
acrylamide and cationic quaternary polyamine, with the lowest charge density.
Therefore, it is the less cationic among the polymers, used as shown in Fig. 3. The
zero EM was obtained with all polymers either at the end of the good clarification,
or at the beginning of the overdose range. The effect of the polymer charge
density was noticed only in the copolymers' case. The Separan Cp-402, which has
a higher charge density than Separan Cp-400, was more effective despite its lower
molecular weight. In the range of the charge densities examined, the differences in
the polyamine charge densities had no systematic influence on the polymers'
optimal dose, or on their corresponding electrophoretic mobilities, as shown in
Fig. 2. The differences noticed between the polyamines and the copolymers with
polyacrylamide in the flocculation curves are as follows:
• The optimal flocculant dose (OFD) of the copolymers was noticeably higher
than that of the polyamines. The optimal dose of Separan Cp-400 was 5.0 £-1 as
compared to 0.6 - 0.8 mg £-1 of the polyamines and 12 mg £-1 of the nonionic polyacrylamide Magnifloc MG202 (Narkis et al. 1990).
• A greater change in EM was obtained with the copolymers than with
.
-1 -1
-1
-1 -1
-1
homopolyammes. EM values of -0.6 /l s V cm and -1.6 /l s V cm were
obtained at the optimal dose for Separan Cp-400 and Cp-402, respectively, as for
the homopolyamines, while no significant change in the EM was noticed at the
optimal flocculant dose.
• The asymptotic values of the EM in the charge reversal region was greater with
the cationic copolymers, particularly with Cp-402, where an asymptotic EM
-1
-f
-1
value of more than +5.0 /l s V cm was obtained. Similar results were
reported by Shun and Gregory (1990).
• In some of the polyarnines' flocculation curves, the turbidity increases steeply
in the overdose range, whereas with the copolymer Separan Cp-402, the turbidity
increases gradually, and with Separan Cp-400 almost no overdose is noticed up