A critical review of waste resources, synthesis, and applications for Zeolite LTA

Accelerated crystallization of magnetic 4A-zeolite synthesized from red mud for application in removal of mixed heavy metal ions.

As a scarce natural resource, the preservation of water quality is of fundamental importance to guarantee its availability for future generations. Due to the increasing industrial activity, effluents are generated with a series of chemical compounds, such as nitrogenous, phosphoric, and organic compounds, heavy metals, and dyes which, if improperly disposed of, contribute to contamination, followed by significant environmental impacts, in addition to the damage to human health. The adsorption technique is an effective approach for removing contaminants from effluents, showing high versatility, due to the use of various materials as adsorbents. Belonging to a wide variety of materials, zeolites reveal to be a promising adsorbent. Zeolites are minerals found in nature or which can be synthesized from industrial residues, standing out in the treatment of contaminated effluents. Zeolite removal efficiency depends on the contaminant to be removed and can reach up to 96% for heavy metals, 90% for phosphoric compounds, 96% for dyes, 80% for nitrogen compounds, and 89% for organics. Aiming at the identification of the more relevant findings and research gaps to advance the use of zeolites in the large-scale treatment of industrial effluents, a review on the recent application of zeolites is needed. This paper presents a global view of zeolites, and a review is conducted on several recent studies using zeolites as adsorbents for the contaminants considered, indicating the main characteristics of the various adsorption systems, demonstrating the particularities of each process, and aiming to reveal useful information to provide future research, in addition to identifying points that need further investigation.

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Zeolite Application in Wastewater Treatment

Bauxite residue (red mud) with a high alumina content requires large amounts of fluxes during smelting, which increases the overall process cost, the energy consumption during smelting, and the acid consumption during slag leaching and decreases the throughput of bauxite residue in the smelting phase. Therefore, alumina was removed (or recovered) from bauxite residue by alkali roasting prior to smelting. The sample after alumina removal could be smelted at 1500 °C without the need of adding any flux to obtain a clear slag–metal separation. After smelting, the slag was leached with acids (HCl, H2SO4, or HNO3). The recovery yields of the rare-earth elements (REEs), except scandium, drastically decreased in the low-alumina slags, compared to the original bauxite residue. These poorer recovery yields are due to the formation of a perovskite (CaTiO3) phase, which binds REEs except scandium. CaTiO3 is a stable phase and does not dissolve in acids under normal conditions. Therefore, slag was quenched to suppress the CaTiO3 formation. The REEs and titanium could also be dissolved in acidic solutions at 25 °C by quenching the molten slag. Removal of alumina from bauxite residue by alkali roasting with sodium carbonate requires high temperatures (>900 °C). Therefore, sodium carbonate was replaced with sodium hydroxide to decrease the energy consumption by decreasing the roasting temperature (<500 °C).

Recovery of Rare Earths and Major Metals from Bauxite Residue (Red Mud) by Alkali Roasting, Smelting, and Leaching

Synthesis of NaY zeolite from coal gangue and its characterization for lead removal from aqueous solution

Feasible conversion of solid waste bauxite tailings into highly crystalline 4A zeolite with valuable application

The invention belongs to the field of aluminosilicate compounds, and in particular relates to a method for preparing a 4A molecular sieve from bauxite tailings. The preparation method comprises the following steps of: (1) iron removal by using an acid process; (2) congruent melting of tailings and alkali; (3) solution preparation; (4) crystallization reaction; and (5) washing. According to the preparation method, the 4A molecular sieve which is suitable for a detergent builder is prepared by taking bauxite milltailings as a raw material, the raw material is abundant in source, and the production cost of the 4A molecular sieve is reduced; and meanwhile, the environment problems caused by low utilization rate and long-term disposal of the bauxite tailings are solved, the utilization rate and the additional value of the bauxite tailings are increased, and a new approach is opened up for comprehensive utilization of the bauxite tailings.

Method for preparing 4A molecular sieve from bauxite tailings

Method for synthesizing corundum-mullite composite phase material by using bauxite tailings

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Feasible conversion of solid waste bauxite tailings into highly crystalline 4A zeolite with valuable application

Method for preparing 4A molecular sieve from bauxite tailings

Method for synthesizing corundum-mullite composite phase material by using bauxite tailings