A comprehensive adsorption study of 1-Hydroxy-2-Naphthoic acid using cost effective engineered materials

TL;DR: In this paper, the authors examined the effect of contact time, contaminant concentration and ionization effects at different pH levels on 1-Hydroxy-2-Naphthoic acid (HNA) adsorption.

Abstract: The naphthoic acids are challenging and costly to remove from water and soil. 1-Hydroxy-2-Naphthoic acid (HNA) is a phenanthrene decomposition product from petroleum-contaminated environments during the aerobic decomposition of polyaromatic hydrocarbons. The hydrogeological mobility of hydrocarbon breakdown products represent a pollution risk (e.g. for drinking water sources). Adsorption to biochar produced from agricultural by-products is a useful strategy to remediate contaminated wastewaters. Here, we examine the controls on the HNA adsorption to the adsorbents magnetite, clay minerals, biochar and magnetite enriched companion materials, namely the influence of contact time, contaminant concentration and ionization effects at different pH. The adsorption of HNA was investigated using low-cost and readily available adsorbents: (i) wheat straw biochar, (ii) rice husk biochar, (iii) sugarcane biochar, (iv) zeolite, (v) montmorillonite, (vi) magnetite and their enriched magnetic companions. Magnetite enriched biochar exhibited greater adsorption rates compared with their nonmagnetic analogs for HNA. The maximum adsorption capacity of the magnetite enriched compounds (initial water concentration of 0.32 mmol HNA.L − 1 ) was 0.45 mmol.HNA.g − 1 of enriched zeolite. The magnetite enriched biochar and conventional biochar showed similar adsorption kinetics although magnetite enrichment improved the efficacy of adsorption. The adsorption fitted the pseudo-second order model in all cases, suggesting the dominant mechanism of adsorption was chemisorption. The magnetite enrichment reduced intra-particle diffusion, possibly due to fouling or blocking of pores within the particles, as evidenced by the decrease in diffusion rate constants. Overall, HNA adsorption improved after magnetic enrichment due to magnetite competing with inhibition sites on the biochar carriers. These findings translate into equivalence between magnetite and magnetic biochars, suggesting cheaper alternative materials could be synthesized in situ with the biochar acting as both an adsorbent and carrier, increasing the prospect of designer biochars for targeted pollutant removal. This approach has the potential to be used for wastewater treatment or for application as a soil additive for remediation of runoff from contaminated soils.

Summary

Introduction

• The naphthoic acids are challenging and costly to remove from water and soil.
• Petroleum hydrocarbons (PH) are widely found pollutants in soil and contaminated water due to their ubiquity and frequency of use (Qadir et al., 2008).
• Wastewaters containing PH are also used for agricultural irrigation creating a pathway for contamination of soil (Feenstra et al., 2000) and accumulation within crops, soil and surface water.
• The authors hypothesis was that magnetite enrichment of biochar and clay minerals would enhance the adsorption properties (number and availability of active sites) of natural biochar adsorbents towards HNA for the remediation of contaminated waters.

2.1. Chemicals

• 1-Hydroxy-2-naphthoic acid, sodium hydroxide (NaOH) both with a purity ≥97 % and hydrochloric acid (HCl) were obtained from Sigma-Aldrich (Islamabad, Pakistan).
• Two types of clay minerals (natural zeolite and montmorillonite), three types of biochars (wheat straw, sugarcane and rice husk biochars) and one iron oxide were used for investigating the sorption of organic pollutants from water.
• Biochar produced by pyrolysis at 350 ⁰C were obtained from NARC (Islamabad, Pakistan).
• Magnetite and natural zeolite were obtained from Meiqi Industry and Trade Co., Ltd (Gongyi City, China) both having a purity of ≥99 percent and particle sizes of 53 and 150 µm respectively.

2.2. Enrichment of biochars and clays with magnetite

• The properties of the magnetite enriched product depend on the enrichment technique and the physical-chemical conditions at which enrichment was carried out.
• Subsequently, sodium hydroxide solution (0.1 M) was added to the magnetite to create a disperse solution of particles which formed a covering layer which was deposited on the surface of each adsorbent particles (visual inspection using microscopy) (Mohan et al., 2014).
• The functionalized mixture (henceforth enriched compound) was filtered and the residue was washed with buffered deionized water (pH 7.0).
• After drying in a laminar flow hood at room temperature, the product of this reaction was stored in air tight bottles.
• The three mixtures prepared were considered magnetite enriched biochars (WSB, SB and RHB).

2.3. Batch experiments

• Batch experiments were performed at ambient temperature (25±2 °C).
• Adsorption of HNA was investigated using both original and magnetite enriched biochars (WSB, RHB and SB), clay minerals, (zeolite and montmorillonite) and magnetite.
• The influence of a number of important process factors were investigated including: contact time of the adsorbent, pollutant concentration and ionization effects at different pH.
• The HNA concentration obtained from spectrophotometric method was validated against appropriate external quality standards for HNA.
• Values obtained from the spectrophotometer were corrected based on the absorbance of double deionized water blanks.

2.4. Adsorption kinetics

• Batch adsorption equilibrium kinetic experiments were carried out in 50 mL total organic carbon (TOC) free borosilicate glass beakers each containing 25 mL of solution at ambient temperature.
• Each experiment was undertaken in triplicate using a HNA solution with a concentration of 0.32 mmolL-1 and 0.05 g of each solid adsorbent material.
• The kinetic data for all the materials tested was evaluated fitting to the pseudo-first order model, the pseudo-second order model and intra-particle diffusion model.
• The linear form of the pseudo-first order model was obtained by integrating and applying the boundary conditions t=0 to t=t and qt=0 to qt=qt (Equation 2).

2.5. Adsorption equilibrium isotherms

• Adsorption equilibrium isotherms were investigated using five different HNA pollutant concentrations at equal intervals between 0.02 and 0.32 mmolL-1, obtained from a single stock solution of HNA.
• To investigate the potential for degradation of HNA, five chemical only blank samples (without solid sorbent material) were placed in covered beakers at room temperature for 3 days (in the dark).
• The adsorption equilibrium isotherm was established by adding 0.05 g each of the solid adsorbent into the HNA solutions having a pH range from 4.5 to 5.3, followed by shaking in the orbital shaker at a rate of 200 rpm at room temperature for 24 hours.
• After 24 hours, samples from each of the solutions were collected by filtering through a sterile polypropylene syringe filter (0.2 µm).
• The remaining concentration of the HNA pollutant in each solution was measured using a UV-visible spectrophotometer as above.

3. Results and Discussion

• The removal of HNA from contaminated water through adsorption is an attractive and low cost method for wastewater treatment (Lu et al., 2010).
• Here, the adsorption of HNA was investigated using three types of biochar, natural materials, magnetite and magnetic companions conducted under a variety of experimental parameters to simulate the range of expected operating parameters (contact time, contaminant concentration and the ionization effects at different pH).

3.1. Adsorption kinetics

• The adsorption behaviour of adsorbents to HNA was assessed at different time intervals, initially the adsorption occurred rapidly up to 180 min of contact time and then increased more gradually until 400 min.
• This is pertinent as the HNA removal character by magnetic biochars was similar to magnetite suggesting this enrichment could be utilized to upgrade the adsorption capacity of local and available biochar.
• The adsorption capacity was in the following sequence and from greatest to least: magnetite > SB > WSB ≈ RHB and after enrichment the adsorption capacity increased but was in the same order of performance.
• The HNA adsorption capacity in order and from greatest to least was: enriched zeolite ≈ enriched montmorillonite >magnetite.

3.2. Kinetic modelling of HNA adsorption.

• The kinetic data was fitted to the pseudo-first order, pseudo-second order and intra-particle diffusion models (Table 1).
• This was evidenced by linear correlation coefficient (r2) values exceeding 0.99 and the closeness of modelled Qe values to the experimental derived Qe values.
• Here, the intra-particle diffusion model revealed that the fastest adsorption rates were observed for WSB and RHB evidenced by Kid values of 0.006 and 0.0067 mmol.[g.min0.5]-1 respectfully (Table 2).
• For example the WSB Kid decreased from 0.006 to 0.005 with similar reductions for other biochar.
• More rigorous stirring or agitation could be used to reduce apparent BLT and potentially increase the rate of diffusion.

3.3. Adsorption equilibrium isotherm

• All adsorbents had lower HNA amounts adsorbed at elevated contaminant concentrations which implies that full saturation of adsorbents’ active sites had occurred preventing further HNA uptake from solution.
• Therefore adsorption was monolayer and chemisorption could not proceed (Singh et al. 2018).

3.4. Impact of pH on adsorption to biochar

• The pH is an important factor on the HNA adsorption process, which influences surface complex reactions which occur at specific mineral adsorption sites (Hanna et al., 2010).
• Previous studies have shown that compounds with stronger electronegativity are bound more strongly to the adsorbent surface which influences the pollutant adsorption rates and regeneration efficacy of adsorbents (Chiou et al., 1979).
• This suggested that the electrostatic attraction between the HNA and the protonated functional groups of the adsorbent increased during each decrease in pH.
• Biochar showed a pronounced decrease in HNA adsorption before enrichment as compared to clay and magnetite adsorption but after enrichment the adsorption behaviour of magnetic biochar decreased more gradually, similar to clay and magnetite for pH, time and concentration of contaminant.
• Further work could investigate the influence of point of zero charge on HNA adsorption and undertake column tests to assess the adsorption using realistic volumes of real water with environmentally relevant concentrations of pollutants.

4. Conclusions

• The batch adsorption data demonstrated that HNA adsorption occurred rapidly before gradual removal occurred which stopped after all the active sites were saturated.
• The HNA adsorption character fitted the pseudo-second order model for all materials tested including enriched and conventional companions, suggesting chemisorption dominated the removal mechanism.
• The removal of HNA was better at lower pH with values of 5-6 being critical for enhancing the activity of key functional groups to reaction with HNA.
• These findings translate into equivalence between magnetite and magnetic biochars, suggesting cheaper alternative materials (to magnetite in isolation) could be synthesized in situ with the biochar acting as a carrier material.
• These findings are of interest to waste and water treatment practitioners interested in low-cost solutions for removal of organic pollutants and their breakdown products.

Figures

Table 1. Kinetic modelling of HNA adsorption to adsorbents

Table 2. Outputs from the intra-particle diffusion model for each adsorbent on HNA

Full text

A Comprehensive Adsorption Study of 1-Hydroxy-2-Naphthoic Acid using Cost Effective
Engineered Materials
Muhammad Aurang Zeb
1
, Ghulam Murtaza
1
, Muhammad Aamer Hussain
1
, Khadija Tul Kubra
2
,
Ralph Muvhiiwa
3,4
, Lueta-Ann De Kock
3
, Francis Hassard
3
,
4,*
1. Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Punjab,
Pakistan.
2. Government College University Faisalabad, Punjab, Pakistan.
3. Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa,
College of Science Engineering and Technology (CSET), UNISA Science Campus, 1710
Roodepoort, Johannesburg, South Africa.
4. Cranfield University, College Way, Bedford, MK43 0AL, UK.
*Corresponding author: Francis Hassard (
francis.hassard@cranfield.ac.uk)
Abstract
The naphthoic acids are challenging and costly to remove from water and soil. 1-Hydroxy-2-
Naphthoic acid (HNA) is a phenanthrene decomposition product from petroleum-contaminated
environments during the aerobic decomposition of polyaromatic hydrocarbons. The
hydrogeological mobility of hydrocarbon breakdown products represent a pollution risk (e.g. for
drinking water sources). Adsorption to biochar produced from agricultural by-products is a useful
strategy to remediate contaminated wastewaters. Here, we examine the controls on the HNA
adsorption to the adsorbents magnetite, clay minerals, biochar and magnetite enriched
companion materials, namely the influence of contact time, contaminant concentration and
ionization effects at different pH. The adsorption of HNA was investigated using low-cost and
readily available adsorbents: i) wheat straw biochar, ii) rice husk biochar, iii) sugarcane biochar,
iv) zeolite, v) montmorillonite, vi) magnetite and their enriched magnetic companions. Magnetite
Environmental Technology & Innovation, Volume 19, August 2020, Article number 100881
DOI:10.1016/j.eti.2020.100881
Published by [Elsevier. This is the Author Accepted Manuscript issued with: Creative Commons Attribution Non-Commercial No Derivatives License (CC:BY:NC:ND 4.0).
The final published version (version of record) is available online at DOI:10.1016/j.eti.2020.100881. Please refer to any applicable publisher terms of use.

enriched biochar exhibited greater adsorption rates compared with their nonmagnetic analogs
for HNA. The maximum adsorption capacity of the magnetite enriched compounds (initial water
concentration of 0.32 mmol HNA.L
-1
) was 0.45 mmol.HNA.g
-1
of enriched zeolite. The magnetite
enriched biochar and conventional biochar showed similar adsorption kinetics although
magnetite enrichment improved the efficacy of adsorption. The adsorption fitted the pseudo-
second order model in all cases, suggesting the dominant mechanism of adsorption was
chemisorption. The magnetite enrichment reduced intra-particle diffusion, possibly due to fouling
or blocking of pores within the particles, as evidenced by the decrease in diffusion rate
constants. Overall, HNA adsorption improved after magnetic enrichment due to magnetite
competing with inhibition sites on the biochar carriers. These findings translate into equivalence
between magnetite and magnetic biochars, suggesting cheaper alternative materials could be
synthesized in situ with the biochar acting as both an adsorbent and carrier, increasing the
prospect of designer biochars for targeted pollutant removal. This approach has the potential to
be used for wastewater treatment or for application as a soil additive for remediation of runoff
from contaminated soils.
Keywords: Enriched adsorbents; zeolite; organic pollutants; biochar; 1-Hydroxy-2-Naphthoic
Acid;
poly aromatic hydrocarbons.

1. Introduction
Inappropriate treatment or disposal of hydrocarbon waste can lead to contamination due to
leaching and transport of organic pollutants into the soil matrix (Mao et al., 2015). Organic
pollutants come from a variety of sources including wastewaters which are derived from food,
leather and textile industries and the petrochemical industry amongst others (Hassard et al.,
2015). Petroleum hydrocarbons (PH) are widely found pollutants in soil and contaminated water
due to their ubiquity and frequency of use (Qadir et al., 2008). Elevated PH concentrations in
industrial wastewater effluents have been reported from low income scenarios (e.g. southern
Punjab) and this polluted water is frequently released to the environment without sufficient
treatment. Wastewaters containing PH are also used for agricultural irrigation creating a
pathway for contamination of soil (Feenstra et al., 2000) and accumulation within crops, soil and
surface water. The accumulation of the PH pollutants within the tissues or on the surfaces of
crops could also promote a human health exposure pathway (Raschid-Sally et al., 2005; Rattan
et al., 2005). The PH are mostly hydrophobic in nature, they are preferentially adsorbed to soil
particles, and they can persist within soils for many years. Clean-up of these contaminated soils
and treatment of run off wastewater is critical to mitigate environmental human health exposure
(Baedecker et al., 1993, Cozzarelli et al., 1994 Das and Mukherjee, 2007). Clearly additional
research is required into novel technologies which can remove PH and their breakdown
products.
The breakdown products of PH are of particular concern as they are predominately polar
chemicals, which are readily water soluble, have high hydrogeological mobility and therefore
elevated pollution potential for groundwater. 1-Hydroxy-2-Naphthoic acid (HNA) is the first
phenanthrene decomposition product in petroleum-contaminated soils during the aerobic
decomposition of polyaromatic hydrocarbons (PAH) and is a widely used surrogate for PAH and

other breakdown products of PH (Hanna and Carteret, 2007; Carney et al. 2008). HNA is not
just a useful surrogate, it is in itself a compound which needs to be treated to reduce the toxicity
of wastewaters. For example, HNA irritates the human respiratory system, causes inflammation
of the eyes and skin and can disrupt normal gut function in humans and animals. Several
studies have shown HNA as a potent inhibitor of intracellular communication and highlighted a
possible role of this compound as a mutagen (Samanta et al., 1999). Quantitative risk estimates
for exposure to HNA are not well defined, however oral exposure is considered one route due to
consumption of contaminated crops or water. The acute oral Lethal Dose 50 (LD
50
) of HNA in
rats was 823-1040 mg.kg
-1
body weight. The no observed effect level (NOEL) for HNA is
considered to be much lower 12-60 mg.kg
-1
body weight per day (European Chemicals Agency,
2019) suggesting removal of HNA from drinking water and soils through treatment is necessary,
particularly in areas prone to high levels of contamination.
Currently, wastewater treatment rely on biological or chemical oxidation processes such as
aerobic or anaerobic bio-treatment, ozone or advanced oxidation processes (Rolph et al., 2018).
These processes are costly are require significant operation and maintenance investment. A
promising route for cost effective remediation of PH breakdown products is
adsorption to natural
or engineered adsorbents (Chen et al., 2011). Natural adsorbents are cheaper and more readily
available than conventional industrial adsorbents such as granular activated carbon (GAC) and
would not require costly regeneration to be effective as additional material can be produced in
situ as required. A diverse range of organic and inorganic contaminants (include PH and HNA)
can be removed using adsorbents such as magnetite and biochar (Cundy et al., 2008; Lu et al.,
2010). Biochar in particular is considered multifunctional and useful for removal of PH
breakdown products from wastewater. Concentration of the pollutant and phase separation
(usually water to solid) could facilitate a safe disposal route, for example incineration (Singh et
al., 2018). Identifying a suitable material which does not create secondary pollution concerns

has proved challenging (Hanna and Carteret, 2007). Recent work has shown the propensity of
‘designer’ or enriched natural materials (where surface area, surface charge or porosity is
altered) to target the specific removal of contaminants for removal of organic pollutants such as
pesticides or PH (Busquets et al., 2014; Rolph et al., 2018; Rolph et al., 2019). Other natural
materials such as the minerals magnetite (Fe
3
O
4
), zeolite and montmorillonite which have high
surface area and ion exchange capacity to remove a wide range of pollutants / ions from
solution (Rashed, 2013). Biochar and iron oxides are readily used separately for the adsorption
of organic pollutants however, their interaction effect requires further study under controlled
conditions. Our hypothesis was that magnetite enrichment of biochar and clay minerals would
enhance the adsorption properties (number and availability of active sites) of natural biochar
adsorbents towards HNA for the remediation of contaminated waters. Studies were done to
assess the removal of HNA under a variety of adsorption conditions and kinetic modeling was
undertaken to assess the dynamic removal rate and permit comparison between materials and
suggest the dominant mechanism(s) of adsorption.
2. Materials and Methods
2.1. Chemicals
1-Hydroxy-2-naphthoic acid, sodium hydroxide (NaOH) both with a purity ≥97 % and hydrochloric
acid (HCl) were obtained from Sigma-Aldrich (Islamabad, Pakistan). Two types of clay minerals
(natural zeolite and montmorillonite), three types of biochars (wheat straw, sugarcane and rice
husk biochars) and one iron oxide (magnetite) were used for investigating the sorption of organic
pollutants from water. Biochar produced by pyrolysis at 350 ⁰C were obtained from NARC
(Islamabad, Pakistan). Magnetite and natural zeolite were obtained from Meiqi Industry and Trade
Co., Ltd (Gongyi City, China) both having a purity of ≥99 percent and particle sizes of 53 and 150