Figure 1.
(A) Sorption of Pb(II) by clinoptilolite as a function of the initial Pb(II) concentration in solution. (B) Sorption isotherm of Pb(II) on clinoptilolite, illustrating the relationship between equilibrium Pb(II) concentration and the amount sorbed.
Table 1.
Results of Pb(II) sorption by natural clinoptilolite
| Initial assumed concentration [mg Pb/L] | Initial measured concentration [mg Pb/L] | Equilibrium concentration [mg Pb/L] | Difference between initial and equilibrium concentration | Amount of Pb [mg] sorbed by 0.8 g of zeolite | Amount of Pb [mg] per 1 kg of zeolite | Pb Removal [%] |
|---|---|---|---|---|---|---|
| 100.0 | 92.0 | 1.6 | 90.4 | 3.6 | 4520.0 | 98.3 |
| 500.0 | 473.4 | <0.5 | 472.9 | 18.9 | 23,645.0 | 99.9 |
| 1000.0 | 966.0 | 7.4 | 958.6 | 38.3 | 47,930.0 | 99.2 |
| 2000.0 | 1948.0 | 355.0 | 1593.0 | 63.7 | 79,650.0 | 81.8 |
| 4000.0 | 3926.0 | 2212.0 | 1714.0 | 68.6 | 85,700.0 | 43.7 |
Figure 2.
XPRD patterns of: (A) Natural zeolite (clinoptilolite) enriched in admixtures of orthoclase (O), illite (I), and quartz (Q), (B) Clinoptilolite after modification through sorption of Pb(II) and (C) Precipitate resulting from reaction of Pb-modified zeolite with AsO43− aqueous solution at pH 7 (50 mg As/L). XPRD, X-ray powder diffraction.
Figure 3.
SEM images in BSE mode display the morphology of Pb-modified clinoptilolite and mimetite precipitates. (A) Pb-modified clinoptilolite, before reaction with an arsenate solution, exhibited a granular surface structure. (B) After reaction with an arsenate solution (50 mg As/L; pH 7) containing Cl− ions (20 mg Cl−/L), mimetite (Pb5(AsO4)3Cl) precipitated. (C) Lead chloro-arsenate formed as needle-like crystals distributed across the surface of the Pb—modified zeolite. (D) These needles developed as incrustations enveloping the grains of the primary Pb-clinoptilolite. (E) The mimetite needles reached lengths of approximately 2.5 μm, exhibiting characteristic hexagonal cross-sections. BSE, backscattered electron; SEM, scanning electron microscopy.
Table 2.
Final concentrations of arsenic (As) and lead (Pb), along with arsenic removal efficiency, after a 7-day reaction between Pb-zeolite and As solution in the presence of chloride ions (20 mg/L)
| Initial pH | Equilibrium pH | Initial [As] = 50 mg/L | ||
|---|---|---|---|---|
| Final [As] mg/L | Removal rate % | Final [Pb] mg/L | ||
| 2.0 | 2.8 | 12.58 | 74.84 | 20.00 |
| 7.0 | 6.3 | 0.07 | 99.88 | <0.02 |
| Initial pH | Equilibrium pH | Initial [As] = 0 mg/L | ||
|---|---|---|---|---|
| Final [Pb] mg/L | ||||
| 2.0 | 2.7 | 42.47 | ||
| 7.0 | 6.4 | 0.61 | ||