Natural zeolite as a chromium VI removal agent in tannery effluents

Abstract

This study concerns Cr(VI) removal using zeolites in a batch system for tannery effluent. In the initial stage, natural zeolite (ZN) and synthetic zeolite (ZS) were characterized, obtaining a Si/Al ratio of 4.64 and 1.60, and with predominant clinoptilolite and faujasite phases, the surface area of 9.34 and 25.82 m 2 /g and cation exchange capacity of 84.05 and 188.72 meq/100 g, respectively. Subsequently, ZN and ZS were activated with HCl and NaOH. Through preliminary tests, with a solution of K 2 Cr 2 O 7 , it was determined that the highest Cr(VI) removal for both, ZN and ZS, was with NaOH activation, obtaining 82 and 56% removal, respectively. According to Ecuadorian regulations, the Cr(VI) concentration exceeds the maximum permissible limits on the tannery effluent. For this effluent, it was determined that the highest Cr(VI) removal, 45%, is obtained with 1 g of ZN activated with NaOH and 100 mL of effluent. With ZN-NaOH, removal tests were carried out in a fixed bed with 5, 10, and 20 g of natural zeolite. The natural zeolite also has chromium removal capacity in the bed system, achieving similar removals to those obtained in the batch experiments, but decreasing the treatment time. Thus, both natural and synthetic zeolites can remove Cr(VI) in tannery effluents, achieving this effluent with permissible limits.

Modification of natural zeolites and their applications for heavy metal removal from polluted environments: Challenges, recent advances, and perspectives

“… Pollutant(s) Environment Zeolite/Treatment Main results References Pb Water natural zeolites (chabazite and clinoptilolite) treatment with 12.1 M HCl solution and heating at 85 °C treatment with HCl eliminated Ca, Mg, Na, K, Al, Fe from the framework Si framework remained intact [ 132 ] Cr Aqueous solution natural zeolite treatment with 0.5 M HCl solution using a 1:3 acid ratio for 1 h at 70 °C and drying at 105 °C and calcination at 350 °C increase in SiO 2 and decrease in Al 2 O 3 content decreased cation exchange capacity due to Al reduction reduction in exchangeable cations due to the removal of Na + , K + , Mg 2+ and Ca 2+ cations the removal percentage of Cr(VI) using NaOH-activated natural zeolite (16 %) was higher compared to HCl-activated zeolite (10 %). [ 133 ] Cd, Cu, Ni, Pb Synthetic aqueous solution clinoptilolite - natural zeolite of 0.71–1.0 mm 2 M HCl, 24 h static conditions efficiency of metals removal was inversely proportional to the metal concentration the adsorption efficiency was Pb 2+ > Cu 2+ > Cd 2+ > Ni 2+ the maximum sorption capacity was 4.22 mg/g for Cd 2+ at an initial concentration of 80 mg/L and 27.7, 25.76, and 13.03 mg/g for Pb 2+ , Cu 2+ and Ni 2+ at an initial concentration of 800 mg/L [ 134 ] Pb, Co, Cr and Zn Aqueous solution washed zeolite mixed with acetic for 1 h and drying at 170 °C for 24 h a removal efficiency of 89.51...…”

Synthesis of Periclase Phase (MgO) from Colloidal Cassava Starch Suspension, Dual Application: Cr(III) Removal and Pigment Reuse

“…In addition, the adsorption capacity of Cr 3+ by MgO can be highlighted by the ion exchange process that occurs when MgO is added to different concentrations of Cr 3+ ion solutions [14]. In Cr(VI) removal studies by Alvares et al [31], zeolites were used in a discontinuous system for tannery effluent, opting for 0.0057 mg/g in the removal tests, with considerably low values. Li et al [32] used mixed aluminum-magnesium hydroxide (AMH) nanoparticles with various molar ratios of Mg/Al prepared by coprecipitation to remove hexavalent Cr, obtaining values of 105.3 to 112.0 mg/g.…”

Column adsorption of biological oxygen demand, chemical oxygen demand and total organic carbon from wastewater by magnetite nanoparticles-zeolite A composite

“…Before now, classical adsorbents namely: zeolites [ 25 ], synthetic resins [ 26 ], biowastes [ 27 ], biochar [ 28 ] and poly (methyl methacrylate) [ 29 ] have been randomly used to decontaminate wastewater. Generally, zeolites are aluminosilicate minerals that are hydrated to be in a microporous structure and used extensively as adsorbent material to remove hazardous contaminants from wastewater [ 30 , 31 ]. However, zeolites and the other identified adsorbents are limited by the difficulty in their separation process.…”