Arsenic Removal Using Iron-Modified Zeolites

Abstract

We determined the ability of two iron-and-zeolite materials to remove arsenic from groundwater. The first material is composed of iron, surfactant-modified zeolite, and hard silicate foam, and is known as Surfactant-Modified Zeolite/ Zero-Valent Iron (SMZ/ZVI). The second material is a new formulation that consists of iron-modified zeolite (IMZ). We prepared eight different prototypes of IMZ for arsenic removal and eventually used one for further testing. The iron content, surface area, and arsenic adsorption capacity were analyzed for each fully prepared material.Lab-based batch experiments were performed on each material to estimate the adsorption capacity. Additionally, the effect of pH on adsorption and the rate of adsorption were determined for the SMZ/ZVI material and one of the newly prepared IMZ. All batch tests were performed using synthetic water based on the chemistry of Socorro Springs water from Socorro, NM. Batch isotherms were performed on each IMZ material using arsenic concentrations that ranged from 10 -200 mg/L. Batch experiments were accompanied by small-scale column experiments in the lab, and in the case of SMZ/ZVI, a field column test was performed at a wellhead. All of the water used in the column experiments was sourced from the Socorro Springs near the city of Socorro, NM (containing 41-45 µg/L arsenate, pH = 8.1, and TDS = 356 µS/cm), and was transported to the lab for column testing. Influent and effluent arsenic concentrations, column flowrates, and total volume were measured in each column study. The measured parameters were used to calculate the volume of water treated below EPA arsenic concentration specifications. All arsenic concentrations were obtained using a hydride generation method coupled with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES).The batch experiments showed that the SMZ/ZVI has a maximum arsenic adsorption capacity as calculated by the Langmuir isotherm of 512 mg/kg. The pH study showed that maximum arsenic adsorption occurs at pH 6.5 and that sorption decreases below or above this pH value. The kinetic studies showed that 95% adsorption is achieved in less than 2 minutes at low concentrations (66 µg/L) and The arsenic adsorption capacity varied greatly between the different types of newly created IMZ and was heavily dependent on the procedures used for iron application. The most successful technique that resulted in good iron coating coverage, robustness, and a high arsenic adsorption capacity was a multi-step process that coated the iron on the zeolite in several smaller amounts rather than one large loading. The material chosen is labeled IMZ-8 and contained 28,400 mg of iron per kg material.Compared with the raw zeolite that had a surface are of 13.8 m²/g, the surface area of IMZ-8 increased about 150% to 21.4 m²/g. Using the Langmuir isotherm, IMZ-8 had a maximum arsenic adsorption capacity of 654 mg/ kg and a Langmuir coefficient of 4.65 L/mg. The IMZ-8 material was further tested by looking at the effects of pH on adsorption an...

Efficiency of Modified Natural Clinoptilolite Tuff for As(III) and As(V) Uptake from Model Polluted Water

“…Within these 700-715 doses, the concentration of arsenic in the effluate spent solution is below the permissible value of 10 μg/L for drinking water. The estimated amount of adsorbed arsenic is about 17 μg/g (Table 2), which is in very good agreement with the results obtained in a study by Andrews (2009). However, this author reaches adsorption of 22 μg/g in the same range of doses but with three times longer contact time.…”

“…The amount of adsorbed arsenic in the batch system from the sorbents Al-Cpt-f, Fe-Mg-Cpt-f, and Fe-Cptf is much greater than the amount of retained arsenic on the corresponding granular sorbents for the same amount of As(III) or As(V) solution (300 ml). Some authors [29] have established similar differences for arsenic adsorption on the two different systems. The high efficiency of the constant volume systems is due to the long contact time between the sorbents and the solutions (in the present study -7h 30min) on the one hand, and on the other hand, due to the small sizes of the sorbents, which provide a large adsorption surface.…”

Efficiency of Modified Natural Clinoptilolite Tuff for As(III) and As(V) Uptake from Model Polluted Water

“…The sorption capacity of similar sorbents varies from about 9 mg/g [17] to 75.4 µg/g [44], corresponding to the specific characteristics of the sorbents and adsorption conditions (for example, the value of 75.4 µg/g is reached at pH = 3). The results obtained by us (17 µg/g) are most comparable with the data for a similar sorbent (22 µg/g) used in similar conditions at three times longer contact time [29]. In the following 633 doses, the efficiency of the sorbent decreases until it is almost completely exhausted.…”