Synthesis and evaluation of zirconia/magnetite/zeolite composite for controlling phosphorus release from sediment: A laboratory study

Highlights

• Zirconia/magnetite/zeolite composite (ZMZ) was used to control P release from sediments.

• ZMZ addition greatly reduced P releasing flux from sediment to overlying water.

• Sediment contact with ZMZ decreased mobile P by changing BD-P to NaOH-rP and ResP.

• Sediment contact with ZMZ reduced bioavailable P including WSP, Olsen-P and AAP.

• Most of P captured by ZMZ is difficult to be re-released into overlying water.

Abstract

Although the conventional zirconium-based solid-phase phosphorus (P)-inactivating agents (ZrPIAs) have high potential for controlling P release from sediments in aquatic systems, they are difficultly retrieved from sediments after their application. Therefore, it is very necessary to develop new ZrPIAs that can be readily retrieved from sediments after their application. In this study, a novel magnetic ZrPIA, i.e., zirconia/magnetite/zeolite composite (ZMZ) was prepared, characterized and used as a sediment amendment to control the release of P from sediments. The adsorption performance and mechanism of phosphate on ZMZ were studied using batch experiments and XPS analysis. The impact of ZMZ addition on the releasing flux of P from sediments to the overlying water as well as on the fractionation and bioavailability of P in sediments was studied using microcosm incubation experiments. In addition, the stability of P captured by ZMZ was also investigated. Results showed that ZMZ exhibited high adsorption ability towards phosphate, with a maximum phosphate adsorption capacity of at least 4.1 mg P/g, and phosphate adsorption onto ZMZ was mainly controlled by inner-sphere complex formation mechanism. The ZMZ addition greatly decreased the releasing flux of P from sediments into the overlying water in anoxic environment, with a DTP (dissolved total P) reduction efficiency of 61.8–97.8%. Moreover, the added ZMZ could immobilize mobile P in sediments by changing P species from Na₂S₂O₄/NaHCO₃-extractable P (BD-P) to NaOH-extractable P (NaOH-rP) and residual P (ResP). Furthermore, the bioavailability of P in sediments could be reduced by the addition of ZMZ. The stability evaluation of P captured by ZMZ after its application showed that a majority of P adsorbed by ZMZ existed in the form of NaOH-rP and ResP, which were difficult to be re-released into the water column under common pH (5–9) and reducing condition. In summary, the above results demonstrate the high potential for the application of ZMZ as an amendment in the control of P release from sediments.

Introduction

It is now generally accepted that phosphorus (P) can contribute to eutrophication of aquatic systems such as rivers, streams and lakes, which is often linked to harmful algal blooms (Chen et al., 2018; Chen et al., 2016; Kõiv et al., 2010; Schindler et al., 2016; Smith et al., 1999). Therefore, in order to struggle against eutrophication of aquatic systems, it is very vital that we take measure to reduce the concentration of P in the overlying water. A range of methods have been developed to control the input of P from the external source into the aquatic system (Andrésa et al., 2018; Liu et al., 2018; Sakadevan and Bavor, 1998; Vohla et al., 2005; Vohla et al., 2011; Yin et al., 2013). However, the effective reduction of external P input does not always lead to the decrease of the P concentration in the overlying water, because the internal P in sediments can be released into the overlying water under certain conditions (Ding et al., 2015; Han et al., 2015a, Han et al., 2015b; Wang et al., 2017b; Zhang et al., 2016; Zhang et al., 2014). Thus, in order to reduce the P level of the overlying water as well as to protect aquatic systems from eutrophication, measures for the reduction of internal P loading are important.

Several restoration strategies have been developed for the control of P release from sediments, including removal of P-rich sediments (sediment dredging) (Jing et al., 2015), nitrate addition (Yamada et al., 2012), aeration (Chen et al., 2011), aluminum inactivation (Lin et al., 2017a), point injection of CaO₂ (Xu et al., 2018), passive capping such as sand, gravel and clay (Kim and Jung, 2010; Xu et al., 2012), and active capping/mixing (Gu et al., 2017; Wang et al., 2017b), etc. In these available methods, in-situ active capping/mixing has drawn a great deal of interest among researchers in recent years as a result of its high efficiency to control P release from sediments. Up to now, plenty of non-magnetic solid-phase P sorbents have been proposed as sediment active capping materials or amendments to prevent P release from sediments, including lanthanum-modified bentonite (Lürling et al., 2016; Lürling and Oosterhout, 2013; Wang et al., 2017b), lanthanum-modified zeolite (Wang et al., 2017c), water treatment residue (Wang et al., 2013), calcite (Berg et al., 2004), calcite/zeolite mixture (Lin et al., 2011), activated carbon (Gu et al., 2017), aluminum-modified zeolite (Gibbs and Özkundakci, 2011), zirconium-based solid-phase P-inactivation agents (ZrPIAs, e.g., zirconium-modified zeolite and zirconium-modified bentonite) (Fan et al., 2017; Lin et al., 2019; Lin et al., 2016; Yang et al., 2014; Yang et al., 2015), thermally-treated calcium-rich attapulgite (TCAP) (Yin and Kong, 2015; Yin et al., 2016), aluminum-modified TCAP (Yin et al., 2018), calcium silicate hydrates (Li et al., 2018a), modified bentonite granular (Liu et al., 2017) and porous ceramic filter media coated with nano‑titanium dioxide film (Wen et al., 2014), etc. However, these non-magnetic active capping materials or amendments are generally suffered from the following problems after their application: (i) due to that they cannot be easily retrieved from the surface water body, capping/mixing technique is specially unfeasible from an economic point of view under a high P-sorbent addition dosage condition; and (ii) if the P-loaded sorbent continue to stay in the surface water body after the use of sorbent in sediment remediation, the P captured by the used sorbent will possibly be re-released into the overlying water in response to the change of future environmental condition (Funes et al., 2017a; Funes et al., 2017b). Therefore, the development of a new active capping material or amendment that can be easily retrieved from the aquatic systems after its application is very necessary.

In recent year, Fe-based magnetic particles (MPs) have emerged as a new amendment to control P release from sediments (Funes et al., 2016; Funes et al., 2017a; Funes et al., 2017b). The biggest advantage of using MPs to control the internal P loading is that the P-loaded MPs can be efficiently recovered from the surface water body by the action of an external magnetic field (Funes et al., 2016; Funes et al., 2017a; Funes et al., 2017b). However, the possible disadvantage of using MPs to control P release from sediment is that Fe is very sensitive to the change in the condition of oxidation-reduction potential and Fe-bound P is easily released back into the overlying water under low redox potential condition over the period of MPs usage (Gao et al., 2016; Reitzel et al., 2013). Therefore, further development of other magnetic particles (the captured P by these magnetic particles is difficult to be re-released into the overlying water under reduction condition during the period of sediment remediation) as active capping material or amendment to control P release from sediments is still very necessary.

Recently, using ZrPIAs as adsorbents to remove phosphate from aqueous solution have caught more and more attention among researchers, because zirconium oxide (active ingredient of ZrPIAs) is environment-friendly, very resistant to oxidants and acid/base, extremely stale in water under conditions of different pH values, and exhibits high adsorption ability for phosphate (Acelas et al., 2015; Lin et al., 2017b; Luo et al., 2017; Shang et al., 2017; Su et al., 2013; Zhang et al., 2017). Furthermore, zirconium-modified zeolite (ZrZeo), one of ZrPIAs, has also been found to be a potential capping material or amendment for controlling phosphorus release from sediment (Fan et al., 2017; Lin et al., 2019; Yang et al., 2014; Yang et al., 2015). One of the main advantages for the use of ZrZeo to control the internal P loading is that most of the bound P by ZrZeo is difficult to be re-released into the water column under reduction conditions (Yang et al., 2015). Therefore, when both magnetite and zirconium are combined with zeolite, the resultant zirconia/magnetite/zeolite composite (ZMZ) may also be a promising capping material or amendment for controlling P release from sediment, because it may be difficult for the adsorbed P by zirconium oxide in ZMZ to be re-released into the water column in a reducing environment and the spent ZMZ may also be effectively retrieved from the surface water body by use of an external magnetic field such as a magnet. However, there is a lack of understanding about the use of ZMZ as a capping material or amendment to control P release from sediments.

The overall goal of the present work was to evaluate the effectiveness of ZMZ addition to control P release from sediments under anoxic condition. The specific objectives of this work were to: (i) study the adsorption performance and mechanism of phosphate from water on ZMZ; (ii) to evaluate the impact of the ZMZ addition on the P flux across the interface between the overlying water and sediment; (iii) to assess the influence of the ZMZ addition on the fractionation and bioavailability of P in sediments; and (iv) estimate the stability of P in ZMZ after its application. Results of this study will contribute to the practical use of ZMZ as a sediment amendment to inhibit the internal P loading of aquatic systems.