Polyacrylamide Soil Conditioners: The Impact …
119
3 PAM Effect on Heavy Metals’ Accumulation in the Soil
Environment
Clays and modified clays have been found particularly useful for adsorption of heavy
metals’ ions and are the objects of several experimental works [99–114]. Clays
mineral due to their internal structure can adsorb metals such as As, Cd, Cr, Co, Cu,
Fe, Pb, Mn, Ni, and Zn from aqueous medium. However, their adsorption capacity
depends on the type of clay used and also differs for various metals [99]. In many
papers, the limiting or enhancing conditions’ effect on the adsorbent efficiency of
the clay materials was studied. The influence of pH value, temperature, quantitative
efficiency of the individual mineral, modifications of the clay, and its composites in
removing various contaminants were examined.
Investigations of pH, contact time, temperature, and initial metal cation concentration influence on uranium(VI) ions’ adsorption on bentonite clay were carried out
[103]. Aytas et al. [103] showed that the mineral adsorption properties can change
due to temperature and time increase—the highest capacity was observed in the case
of bentonite calcinated under 400 °C and at the beginning of adsorption process.
Mishra and Patel [104] studied lead and zinc ions’ removal from water by various
adsorbents, i.e., kaolin and bentonite depending on the time, pH, adsorbent dosage,
and contact time. The obtained results showed no significant differences in heavy
metals adsorption in various pH values. The highest Pb and Zn removal from solution
was observed when an increase in adsorbent dosage occurred. The increase of ionic
strength of electrolyte results in decrease of metal ion adsorption.
The removal of Pb, Cd, Ni, and Cu ions from aqueous solution by kaolinite was
studied by Jiang et al. [111]. The adsorption was carried out in different conditions
differing with initial metal ion concentration, pH, ionic strength of electrolyte, and
contact time. Obtained results showed that the pH value of solution had most significant impact on heavy metal adsorption on clay surface, and adsorption equilibrium
was obtained after 30 min. With the increasing metal concentration, its adsorption
also increases (due to stronger driving forces to mineral surface).
Bhattachryya and Sen Gupta [100] reviewed the removal of toxic metal ions by
natural kaolinite, montmorillonite, and their modified forms by pillaring with polyoxy
cations such as Zr
4+ , Al
3+ , Si
4+ , Ti
4+ , Fe
3+ , Cr
3+ , and Ga
3+ . Comparison of adsorption
capacity of these adsorbents indicated that the natural and modified montmorillonite
may adsorb much more heavy metals than kaolinite sorbents. Various metal ions
can be captured from solution by clay mineral adsorbent and their modified forms
[99]. The sorption affinity to As anions improvement by pre-treatment of kaolin or
bentonite minerals with Fe(II), Fe(III), Al(III), and Mn(II) ions was shown [107].
Na et al. [109] demonstrated that by pillaring Ti to montmorillonite, the arsenate or
arsenite removal efficiency from aqueous solution can be increased. The adsorption
of As ions as a function of pH value, contact time, temperature, coexisting ions’
presence, and ionic strength was studied. Comparing all examined ions (phosphate,
119
3 PAM Effect on Heavy Metals’ Accumulation in the Soil
Environment
Clays and modified clays have been found particularly useful for adsorption of heavy
metals’ ions and are the objects of several experimental works [99–114]. Clays
mineral due to their internal structure can adsorb metals such as As, Cd, Cr, Co, Cu,
Fe, Pb, Mn, Ni, and Zn from aqueous medium. However, their adsorption capacity
depends on the type of clay used and also differs for various metals [99]. In many
papers, the limiting or enhancing conditions’ effect on the adsorbent efficiency of
the clay materials was studied. The influence of pH value, temperature, quantitative
efficiency of the individual mineral, modifications of the clay, and its composites in
removing various contaminants were examined.
Investigations of pH, contact time, temperature, and initial metal cation concentration influence on uranium(VI) ions’ adsorption on bentonite clay were carried out
[103]. Aytas et al. [103] showed that the mineral adsorption properties can change
due to temperature and time increase—the highest capacity was observed in the case
of bentonite calcinated under 400 °C and at the beginning of adsorption process.
Mishra and Patel [104] studied lead and zinc ions’ removal from water by various
adsorbents, i.e., kaolin and bentonite depending on the time, pH, adsorbent dosage,
and contact time. The obtained results showed no significant differences in heavy
metals adsorption in various pH values. The highest Pb and Zn removal from solution
was observed when an increase in adsorbent dosage occurred. The increase of ionic
strength of electrolyte results in decrease of metal ion adsorption.
The removal of Pb, Cd, Ni, and Cu ions from aqueous solution by kaolinite was
studied by Jiang et al. [111]. The adsorption was carried out in different conditions
differing with initial metal ion concentration, pH, ionic strength of electrolyte, and
contact time. Obtained results showed that the pH value of solution had most significant impact on heavy metal adsorption on clay surface, and adsorption equilibrium
was obtained after 30 min. With the increasing metal concentration, its adsorption
also increases (due to stronger driving forces to mineral surface).
Bhattachryya and Sen Gupta [100] reviewed the removal of toxic metal ions by
natural kaolinite, montmorillonite, and their modified forms by pillaring with polyoxy
cations such as Zr
4+ , Al
3+ , Si
4+ , Ti
4+ , Fe
3+ , Cr
3+ , and Ga
3+ . Comparison of adsorption
capacity of these adsorbents indicated that the natural and modified montmorillonite
may adsorb much more heavy metals than kaolinite sorbents. Various metal ions
can be captured from solution by clay mineral adsorbent and their modified forms
[99]. The sorption affinity to As anions improvement by pre-treatment of kaolin or
bentonite minerals with Fe(II), Fe(III), Al(III), and Mn(II) ions was shown [107].
Na et al. [109] demonstrated that by pillaring Ti to montmorillonite, the arsenate or
arsenite removal efficiency from aqueous solution can be increased. The adsorption
of As ions as a function of pH value, contact time, temperature, coexisting ions’
presence, and ionic strength was studied. Comparing all examined ions (phosphate,