Table 8.

A summary of other treatment methods of zeolites for heavy metals removal from environment.

Pollutant(s)	Environment	Zeolite/Treatment	Main results	References
Ni	Aqueous solution	•natural zeolite with particle size of 0.3–0.5 mm •treated separately with 1 M NH3, 1 M NaOH and 1 M NaCl solutions at pH = 5, sorbent dosage 4 g/L, contact time 30 min, room temperature	•sorption capacity increased in the following order: NH3-treated zeolite (9.9 ± 0.6) < natural zeolite (19.7 ± 0.3) < NaOH-treated zeolite (24.0 ± 0.9) < NaCl-treated zeolite (28 ± 2) mg⋅g−1	[145]
Pb2+, Zn2+, Ni2+, Cr3+	Solution	•zeolite X, sodalite, and zeolite A obtained from natural sources: bauxite, and obsidian	•removal >96 % for Pb2+, Zn2+, and Cr3+ and around 70 % of Ni2+ for all the investigated zeolites	[148]
Hg	Water	•Na-zeolite prepared by mixing 100 g natural zeolite with to 1 M NaCl at 60 °C, 7 days •the Ag exchanged zeolite was obtained by mixing Na-form of the zeolite with 0.1 M AgNO3 solution at room temperature, for 24h, under dark conditions	•natural zeolite was effective in removing Hg from Hg(NO3)2 solutions, but was not effective in removing Hg from HgCl2 solutions •natural Ag-zeolite was also efficient for Hg removal from HgCl2 solutions	[149]
Ni	Aqueous solution	•mordenite-type natural zeolite modified (fraction <125 μm) in Na form •zeolite treated with 1 M HNO3 to remove impurities, then immersed in a 5 M NaCl solution, for 8 days	•a material with high specific surface area (SBET = 124.95 m2/g) and total pore volume of 0.45 cm3/g •a maximum adsorption capacity of 36.79 mg/g at 60 °C for Ni, obtained by the Langmuir isotherm	[150]
Cr(VI)	Solution	•natural zeolite heated at 110 °C for 3h, activated by 2 M of HCl for 24 h •activated zeolite was modified with FeCl3 solution in different ratios	•modified zeolite reduced Cr(VI) concentration from artificial solution from 70 mg/L to 0.24 mg/L, achieving an 87 % removal rate •a removal efficiency of 93.33 % after 4 h contact time	[151]
Cd	Aqueous solution	•natural zeolite treated with a 2 M NaCl solution for 24 h	•Cd adsorption on zeolite increased with increase in initial Cd concentration	[152]
Ca/Mg (hardness)	Groundwater	•natural zeolite mechanically activated at different periods of time (2 h, 4 h, 6 h, 8 h) at 600 rpm	•natural zeolite significantly improved adsorption capacity with enhancing the activation time by 2 h (296 mg/g), 4 h (367 mg/g), 6 h (392 mg/g), and 8 h (450 mg/g)	[153]
Hg	Aqueous solution	•clinoptilolite-natural zeolite, fraction 0.6–0.8 mm, modified with Fe on 3 stages: mixed with a 1 M Fe(NO3)3·9H2O, 1 M NaOH and 4 % NaNO3 solution and dried at 40 °C	•sorption of Hg(II) was highly sensitive to the effect of pH •the removed amount of Hg by modified zeolite (0.54 mmol Hg/g) was twice higher than onto unmodified natural zeolite (0.28 mmol Hg/g)	[147]
Cd	Aqueous solution	•philipsite rich natural zeolite with grain size of 0.595–1.41 nm shaken with 2 N NaCl or CaCl2 for 24 h	•Na treated zeolitic tuff has the maximum exchange capacity than other types of calcium and acid treated zeolites •zeolite structure is damaged at pH = 1–2 as removal efficiency becomes unremarkable	[154]
Pb, Cu, Zn and Cd	Sediment	•natural zeolite of different grain size was immersed in a solution of 2 M NaCl at 75 °C for 3 h •centrifugation and drying at 105 °C for 3h	•NaCl-modified zeolite displayed the highest CEC and metal sorption compared with acid (2 N HCl) and alkaline (2 N NaOH)-modified zeolite, under the same experimental conditions	[80]