Adsorptive Removal of Phosphate from Aqueous Solutions Using Low-Cost Volcanic Rocks: Kinetics and Equilibrium Approaches

Abstract

The contamination of surface and groundwater with phosphate originating from industrial and household wastewater remains a serious environmental issue in low-income countries. Herein, phosphate removal from aqueous solutions was studied using low-cost volcanic rocks such as pumice (VPum) and scoria (VSco), obtained from the Ethiopian Great Rift Valley. Batch adsorption experiments were conducted using phosphate solutions with concentrations of 0.5 to 25 mg·L−1 to examine the adsorption kinetic as well as equilibrium conditions. The experimental adsorption data were tested by employing various equilibrium adsorption models, and the Freundlich and Dubinin-Radushkevich (D-R) isotherms best depicted the observations. The maximum phosphate adsorption capacities of VPum and VSco were calculated and found to be 294 mg·kg−1 and 169 mg·kg−1, respectively. A pseudo-second-order kinetic model best described the experimental data with a coefficient of correlation of R2 > 0.99 for both VPum and VSco; however, VPum showed a slightly better selectivity for phosphate removal than VSco. The presence of competitive anions markedly reduced the removal efficiency of phosphate from the aqueous solution. The adsorptive removal of phosphate was affected by competitive anions in the order: HCO3− >F− > SO4−2 > NO3− > Cl− for VPum and HCO3− > F− > Cl− > SO4−2 > NO3− for VSco. The results indicate that the readily available volcanic rocks have a good adsorptive capacity for phosphate and shall be considered in future studies as test materials for phosphate removal from water in technical-scale experiments.

A Sustainable Solution to Obtain P-K-Mn Glass Fertilizers from Cheap and Readily Available Wastes

“…The very good linearity of the q t = f(t 1/2 ) plots is highlighted by the values of the coefficients of determination over 0.95, confirming the applicability of the intraparticle diffusion model to describe the ions dissolution. This behavior, previously mentioned in literature [49,50], indicates that two processes influence the ion leaching in the citric acid solution. The first corresponds to the diffusion through the vitreous matrix and the second to the diffusion through the glass particle-medium interface.…”

Fixed-Bed Column Technique for the Removal of Phosphate from Water Using Leftover Coal

“…In the present study, phosphate removal potential was examined in a fixed-bed column by using leftover coal material. The same authors verified the application of leftover-coal [ 31 ] and volcanic-rock [ 22 ] material as potential adsorbents for the recovery of phosphate from an aqueous solution through classical slurry batch experiments. However, batch-adsorption data are inconvenient for large-scale volumes due to the overestimation of sorption capacities [ 32 ].…”

“…The column was packed with a known amount of adsorbent material (leftover coal) to achieve the intended bed heights (5 to 8 cm), and then caped at the top and at the bottom with glass wool to avoid bed height changes due to the loss of some adsorbents and to prevent adsorbent wash out. Artificial phosphate-laden wastewater was synthesized by previously diluting phosphate stock solution with a concentration of 1000 mg/L to the working solution at concentrations of 10 to 25 mg/L using distilled water, and the pH of each working solution was adjusted to 3.5 using HCl and NaOH by pH meter according to our previous works [ 22 , 31 ]. Depending on the pH of the working solution, phosphorus can be present in the solution in the form of H 3 PO 4 , H 2 PO 4 − , HPO 4 2− , and PO 4 −3 .…”

“…Adsorption has received immense interest due to its high removal efficiency, simple operation, better cost effectiveness, less or no sludge production, and invulnerability to coexisting pollutants [ 18 , 19 , 20 ]. The application of low-cost and locally available materials for phosphate removal was widely investigated during this decade, such as with modified biochar [ 20 ], steel slag [ 21 ], volcanic rock [ 22 ], alkaline Tunisian soil [ 23 ], chitosan composite [ 24 ], alum sludge [ 25 ], and furnace slags [ 26 ].…”

Determination and Removal of Phosphate and Nitrate from the Ground and Surface Water at the Three Counties of Guyana

“…Biftu et al [20] have studied the adsorption of phosphate, nitrate, and chromate through adsorption on activated carbon derived from the stem of the Carissa Carandas plant. Phosphate removal from aqueous solution was studied by Mekonnen et al [21] using low-cost volcanic rocks such as pumice and scoria obtained from the Ethiopian Great Rift Valley. Phosphate removal and recovery from wastewater using layered zinc hydroxide as an adsorbent were investigated by Almasri et al [22].…”