Hydroxyapatite Coatings on Calcite Powder for the Removal of Heavy Metals from Contaminated Water

Oriol Gibert,Rosa Mari Darbra,Josep Oliva Moncunill,María M Martínez,César Valderrama,Vicenç Martí

doi:10.3390/w13111493

Oriol Gibert, Rosa Mari Darbra + Show 4 more

Open Access

https://doi.org/10.3390/w13111493

Copy DOI

Abstract

An approach for the remediation of heavy metal-contaminated wastewater that is gaining increasing attention is the application of hydroxyapatite (HAP)-based particles. HAP is conventionally synthesized through wet chemical precipitation of calcium and phosphate ions, although later studies have focused on HAP synthesis from solid calcite contacted with a phosphate solution under ambient conditions. This synthesis route can allow saving soluble Ca-chemicals and, thus, make the process more cost-efficient. The aim of this study was to coat natural calcite powder with a layer of HAP for the removal of Zn and Cu from contaminated water. For this purpose, a HAP layer was synthesized on calcite particles, characterized using several complementary techniques and evaluated for the removal of Zn and Cu from synthetic solutions. Sorption kinetics and equilibrium isotherms, as well as the effect of sonication of the synthesized sample on its sorption performance, were determined. The results showed that calcite particles were efficiently coated with a HAP layer with high capacity in removing Zn and Cu from acidic solutions, with a qmax of 34.97 mg/g for Zn (increased to 37.88 g/mg after sonication of the sample) and 60.24 mg/g for Cu (which hardly varied with sonication). The mechanisms behind the sorption of Zn and Cu onto HAP, inferred from pH changes, the relation between metal uptake and Ca2+ release and XRD analysis, included surface complexation, ion exchange and precipitation of new Zn- and Cu-containing phases.

Highlights

Acidic metal-rich wastewater from mining and industrial processes represents an environmental problem worldwide due to its low pH and high content of heavy metals.It is well-known that heavy metals discharged into the environment may pose a serious hazard to all living beings because of their bioaccumulation and toxicity even at low concentrations [1,2]
HAP is conventionally synthesized through wet chemical precipitation of calcium and phosphate ions, later studies have focused on HAP synthesis from solid calcite contacted with a phosphate solution under ambient conditions
At 1810 cm−1 was observed coming from stretching vibration ν(C=O), while the slight shoulder at 1060 cm−1 can be ascribed to symmetrical stretching ν(C–O) [37,39]

Summary

Introduction

Acidic metal-rich wastewater from mining and industrial processes represents an environmental problem worldwide due to its low pH and high content of heavy metals.It is well-known that heavy metals discharged into the environment may pose a serious hazard to all living beings because of their bioaccumulation and toxicity even at low concentrations [1,2]. Acidic metal-rich wastewater from mining and industrial processes represents an environmental problem worldwide due to its low pH and high content of heavy metals. The removal of heavy metals in these systems can be achieved through several processes, with the most common ones being chemical precipitation, coagulation-flocculation, membrane filtration, ion-exchange, electrochemical processes and sorption. Ion-exchange has proved to be useful for the removal and recovery of heavy metals from water. It offers the advantages of selective removal and no sludge production, but on the other hand, ion-exchange resins are expensive and their regeneration can increase the cost even further. Sorption arises as one of the most attractive methods thanks to its efficiency, versatility, simplicity in design and operation and low cost [5,9]

Objectives

Methods

Results

Conclusion