5.2
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Corrigendum
Current Issue
Editorial
Erratum
Full Length Article
Full lenth article
Letter to Editor
Original Article
Research article
Retraction
Retraction notice
Review
Review Article
SPECIAL ISSUE: ENVIRONMENTAL CHEMISTRY
5.3
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
Corrigendum
Current Issue
Editorial
Erratum
Full Length Article
Full lenth article
Letter to Editor
Original Article
Research article
Retraction
Retraction notice
Review
Review Article
SPECIAL ISSUE: ENVIRONMENTAL CHEMISTRY
View/Download PDF

Translate this page into:

Original article
12 (
8
); 3141-3150
doi:
10.1016/j.arabjc.2015.08.006

Removal of heavy metals from waste phosphogypsum materials using polyethylene glycol and polyvinyl alcohol polymers

, ,
a College of Engineering, Muzahimiyah Branch, King Saud University, P.O. Box 2454, Riyadh 11451, Saudi Arabia
b Present address: College of Engineering, Muzahimiyah Branch, King Saud University, Riyadh, Saudi Arabia
c Permanent address: Department of Chemical Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, Ma'an, Jordan
d Department of Environmental Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, Ma'an, Jordan

⁎Corresponding author. Present address: College of Engineering, Muzahimiyah Branch, King Saud University, P.O. Box 2454, Riyadh 11451, Saudi Arabia. Tel.: +966 11 4677996; fax: +966 11 46733561; Permanent address: Department of Environmental Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, P.O. Box (20), Ma'an, Jordan. Tel.: +962 3 2179000; fax: +962 3 2179050. malhwaiti@ksu.edu.sa (Mohammad Al-Hwaiti) mohhwaiti@ahu.edu.jo (Mohammad Al-Hwaiti)

Received: , Accepted: ,
© The Author(s) 2015
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Enormous stockpiles of phosphogypsum (PG) generated during the wet process production of phosphoric acid are stored at many sites around the world and pose problems for their safe storage, disposal, or utilization. The aim of this study was to investigate the performance of two polymers polyethylene glycol (PEG) and polyvinyl alcohol (PVA) in removing heavy metal from waste PG materials with a batch reaction approach. Batch experiments showed that the adsorption capacities of PEG and PVA polymers increased quietly as a result of molecular weight with increase in active surfaces of adsorbents. It is important to note that the adsorption capacities of the PEG and PVA polymers presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of molecular weight, and the concentration of adsorbate. The maximum percentage removal with PEG of Cd, Cr, Cu, Pb, Zn, and Mo followed the order: Cu (96%) > Cr (94%) = Mo (94%) > Zn (74%) > Cd (70%) > Pb (11%), while the removal of Cd, Cr, Cu, Mo, Pb, and Zn with PVA adsorbents followed the order: Cu (95%) > Mo (93%) > Cr (91%) > Cd (84%) > Zn (78%) > Pb (10%). Obviously, PEG and PVA polymers are suitable for industrial hazardous solid waste containing Cd, Cr, Cu, Mo, Pb, and Zn contaminations. The calculated singular indices including ecological risk factors (Eri) showed that Cd should be considered a moderate potential ecological risk, while Cr, Cu, Pb, and Zn indicated a low ecological risk. The calculated integrated potential ecological risk indices (RI = ∑Eri) considered that Cd, Cr, Cu, Pb, and Zn indicated pollution in all studied samples is less. Among these results, Cd, Cr, Cu, Pb, and Zn content removal using PEG and PVA polymers would be of great importance in environmental applications, and they can be considered a very suitable and efficient option for PG utilization.

Keywords

Phosphogypsum
Mobility of heavy metal
Polyethylene glycol
Polyvinyl alcohol
Ecological risk assessment
1

1 Introduction

Phosphogypsum (PG) is a waste by-product of the wet process of phosphoric acid production, which contains variable amounts of some impurities such as naturally occurring radionuclides, fluoride, and heavy metals depending on the source (Rutherford et al., 1996; Al-Hwaiti et al., 2013). About 5 tonnes of PG are generated for every tonne of phosphoric acid (H3PO4) manufactured. The operative chemical reaction is generalized as

(1)
Ca 5 ( PO 4 ) 3 F + 5 H 2 SO 4 + 10 H 2 O → 3 H 3 PO 4 + 5 CaSO 4 · 2 H 2 O + HF

At present, worldwide production of PG is over 100–280 Mt/a (Parreira et al., 2003). Only 14% of the worldwide production is reprocessed, 28% is dumped into water bodies, and 58% is being stockpiled and may cause huge environmental problems (Carmichael, 1988).

Studies have been conducted on the beneficial ways of utilizing PG in order to reduce the disposal problem and the environmental implications. These include uses of PG: (1) agricultural fertilizer or for soil stabilization amendments (Al-Oudat et al., 1998; El-Mrabet et al., 2003), (2) cement industry as a setting regulator in place of natural gypsum (Potgieter et al., 2003), in the gypsum industry to make gypsum plaster (Papastefanou et al., 2006; Garg and Jain, 2010), as mineralizer in the burning Portland cement clinker (Van der Merwe and Strydom, 2004; Kacimi et al., 2006), as raw material in the raw mix of cement (Singh, 1987; Ali, 2004), and in other binder materials (Singh et al., 1996; Taher, 2007). Tayibi et al. (2009), reported a preliminary study of a PG stabilization process using a sulfur polymer matrix in order to improve mechanical properties of PG concretes. Results show a new PG concrete product with good mechanical properties and low radionuclide contents, and it can be considered a very suitable and efficient option for PG disposal.

Polymer–metal ion interactions are a subject of great interest as they have potential analytical and technological applications in fields such as environmental science, industrial effluent treatment, and the metallurgy industry (Mamta et al., 2012). By increasing downstream industry, heavy metal ions undergo several technical processes and finally fate of effluent, solid waste, sewage, dumps and dust, into the water, the earth and the air and thus into the food chain as finely dispersed and/or in solutions.

In this sense, numerous research efforts are being done to develop methods to remove heavy metal ions, particularly in waste streams of hydro-metallurgy and related industries, and to subsequently reuse them. These techniques include filtration, chemical precipitation, neutralization, reverse osmosis and electrolysis, chelating ion exchange and adsorption (Zamzow and Murphy, 1992; Rivas et al., 2001; Dabrowski et al., 2004; Hema et al., 2011; Nasef and Güven, 2012).

Among these techniques, utilizing chelating polymers was of great importance in environmental applications (Yahia et al., 2013); for example, biosorption of heavy metal using polyvinyl alcohol (PVA) for immobilization has long been reported and includes immobilized enzymes (Imai et al., 1986; BAI and Abraham, 2003). Eisazadeh (2007), reported the removal of heavy metals from water and wastewaters using conductive electroactive polymers such as polypyrrole and polyaniline, and the removal of arsenic in wastewater using poly ethylene glycol (PEG) and its composites in the presence of FeCl2 as an oxidant has been employed (Eisazadeh, 2008).

Reverse osmosis has been also applied in the removal of chromium from wastewater (Selvaraj et al., 1997). The removal of nonpolar organic material from water and wastewater using activated carbon has been adapted by Ying et al., (1990), whereas the removal of heavy metals from water and wastewaters using bentonite has been a topic of Christids et al. (1997). Nevertheless, these methods used for the removal of heavy metals, may be efficient but expensive (Hema et al., 2003).

As mentioned above, a number of workers have used different adsorbent systems, developed from various industrial waste materials, for the removal of heavy metals. There still exists a need to develop a low cost and efficient adsorbent for the removal of heavy metals from solid waste. However, the commercial use of PG in Jordan is currently limited to the production of cement, as agriculture and soil amendment (Al-Hwaiti et al., 2010). In the present work, an attempt has been made to utilize an inexpensive adsorbent system for the removal of heavy metals from PG using PEG and PVA. The objective of the present study was to investigate the performance of two polymers (PEG and PVA) in removing heavy metal from PG with a batch reaction approach. The effectiveness of the adsorbent comprises polyethylene glycol (PEG) which has the following structure:

and polyvinyl alcohol (PVA) which has the following structure:

The purpose of using these polymers is that (1) they have unpaired electrons while the heavy metals have valence shells and by the 18-electron rule the unpaired electrons will bond with these shells and remove it from water. Further, these polymers are cheap and available and (2) to determine influence of PEG molecular weight and PVA molecular weight in removing heavy metal from waste PG materials and their influence on heavy metals risk assessment to assess safe use of purification PG in agriculture and soil amendment.

2

2 Materials and methods

2.1

2.1 Materials

Phosphogypsum samples were taken from the stacks in Ehidiya Mines area, Jordan (Fig. 1). The representative samples were selected, ground, dried overnight at 45 °C, and then carried out for leaching experiments. 2 g of PG was used in each leaching test.

Sampling collection and location map of the study area.
Figure 1 Sampling collection and location map of the study area.

2.2

2.2 Leaching experiments

Leaching experiments were conducted with polyethylene glycol (PEG) and polyvinyl alcohol (PVA) to determine concentrations of heavy metals that are released from PG to the aqueous phase. Four kinds of polymers with different weight average molecular weights were applied as follows: (PEG-1, MW = 10,000), polyethylene glycol (PEG-2, MW = 35,000), polyvinyl alcohol 80% hydrolyzed (PVA-1, MW = 9500), and polyvinyl alcohol 87–89% hydrolyzed (PVA-2, MW = 18,000). These polymers were obtained from Merck, Germany, and used without purification. Distilled water was used as dispersing medium.

PEG and PVA were used as polymers. The reaction was carried out in an aqueous media at room temperature for 4 h. Total 2.2 g of PEG and PVA was used for leaching test. Masses of 0.5 g, 0.7 g and 1 g were weighed and volumes of 100 ml of distilled water were added to each experiment to produce surfactant solutions. The surfactant solution was then added followed by 2 g of PG for each test, assuring that the solid always remained in suspension. Important parameters, such as, room temperature of 30 °C, leaching duration of 24 h, and liquid/solid (L/S) ratio influencing the leaching process, were investigated in order to obtain metal concentrations as high as possible or select optimal parameters for the leaching process. Finally, the mixing products of PG and surfactant solutions were then separated by centrifugation at 3000 rpm for 5 min. The extract was decanted and filtered through 0.45 μm filter paper. The treated PG mass was dried overnight at 65 °C, and then analyzed by AAS analysis. Each test was conducted simultaneously in triplicate and results were averaged for data analysis.

2.3

2.3 Chemical analysis

Digestions were performed on 15 samples in triplicate. 1 g of each PG sample was put in Teflon beakers, to which 5 ml of aqua regia (3 ml of conc. HCl and 2 ml conc. HNO3) was added before allowing the reaction to subside. This was followed by the addition of 2 ml conc. HNO3. Samples were then taken to dryness on a hotplate at 110 °C. A further 1 ml of conc. HNO3 was then added and the sample was again taken to dryness. Dried samples were then removed from the hotplate and cooled, 19 ml of 1% HNO3 was added, and the solution was heated in an oven at 100 °C for 30 min. The concentrations of Cd, Cr, Cu, Ni, Pb, V, and Zn were measured using an atomic absorption spectroscopy (AAS, Model Perkin Elmer A800 “Graphite and Flame”, Varian, USA) at Bin Hayyan-Aqaba International Laboratories Management, Aqaba Special Economic Zone Authority (ASEZA), Jordan. Quality assurance and control were assessed using the duplicates and blanks method, prepared in the laboratory following the procedures as described in Method ISO 11466 (ISO 11466, 1995).

2.4

2.4 Calculating heavy metals removal

The percentage of metals removed and leached from the PG during the batch reaction experiments. The % removal of the elements was calculated based on the following equation:

(2)
% Removal ( % R ) = C i - C f C i × 100
(3)
% Leachable ( % L ) = C f C i × 100 where Ci is the initial concentration in mg/kg, and Cf is the final concentration in mg/kg.

2.5

2.5 Risk assessment

Potential ecological risk index is a powerful tool for processing, analyzing, and conveying raw environmental information to decision-makers, managers, technicians, and the public (Hakanson, 1980). The heavy metal i.e. Cd, selected in this investigation is because of its interest from environmental and biological points of view (Mamta et al., 2012). Nowadays, Cadmium is regarded as the most serious contaminant of water, soil, sediment, and plants. Caeiro et al. (2005), used ecological risk indices to assess heavy metal pollutions in the ecosystem. In this study, potential ecological risk index was assessed.

In this study, the assessment of ecological risk (RI) of Cd, Cr, Cu, Pb, and Zn in PG was carried out by using the potential ecological risk index (RI) proposed by Hakanson (1980):

(4)
RI = ∑ i = 1 n Er i = ∑ i = 1 n Tr i xC f i = ∑ i = 1 n T r i x ( C n i / C o i )

RI is the sum of the single ecological risk factors (Eir) of five pollutants, Cd, Cr, Cu, Pb, and Zn. In this study, the single potential ecological risk factor (Eir) of Cd, Cr, Cu. Pb, and Zn was calculated. Tir is the metal toxic response factor according to Hakanson (1980); the values for Cd, Cr, Cu. Pb, and Zn were 30, 2, 5, 5, and 1 (μg/g), respectively. Cif is the single pollution index which is equal to the ratio of the metal toxic concentration in samples (Cin) to the background value (Cio) of Cd, Cr, Cu. Pb, and Zn i.e. 1, 90, 50, 70, and 175 (μg/g) respectively in the pre-industrial reference (Hakanson, 1980; Xu et al., 2008). The potential ecological risk (RI) degree of a given region was divided into 4 grades: RI < 150, low ecological risk; 150 ⩽ RI < 300, moderate ecological risk; 300 ⩽ RI < 600, considerable ecological risk; and RI ⩾ 600, very high ecological risk. The following terminologies are used to describe the risk factor: Eri < 40, low potential ecological risk; 40 ⩽ Eri < 80, moderate potential ecological risk; 80 ⩽ Eri < 160, high potential ecological risk; 160 ⩽ Eri < 320, very high potential ecological risk; and Eri ⩾ 320, extremely high potential ecological risk.

3

3 Results and discussion

3.1

3.1 Effect of heavy metals

The heavy metals (mg kg−1) removal capacities and selectivity properties of PEG-1, PEG-2, PVA-1 and PVA-2 polymers in PG are shown in Table 1.

Table 1 The heavy metals (mg kg−1) removal capacities and selectivity properties of PEG-1, PEG-2, PVA-1 and PVA-2 polymers in PG.
Element Dosage 0.5 (g) Dosage 0.7 (g) Dosage 1 (g)
T CX %L %M T CX %L %M T CX %L %M
PEG-1
Cd 2.81 1.59 56.58 43.42 2.81 1.7 60.50 39.50 2.81 1.82 64.77 35.23
Cr 52 42.75 82.21 17.79 52 43.64 83.92 16.08 52 45 86.54 13.46
Cu 10.9 10.2 93.58 6.42 10.9 10.3 94.50 5.50 10.9 10.46 95.96 4.04
Pb 0.5 0.039 7.80 92.20 0.5 0.043 8.60 91.40 0.5 0.052 10.40 89.60
Zn 46 27.8 60.43 39.57 46 30.56 66.43 33.57 46 31.46 68.39 31.61
Mo 17 13.79 81.12 18.88 17 14 82.35 17.65 17 14.57 85.71 14.29
  PEG-2
Cd 2.81 1.85 65.84 34.16 2.81 1.89 67.26 32.74 2.81 1.95 69.40 30.60
Cr 52 48.78 93.81 6.19 52 47.4 91.15 8.85 52 48.8 93.85 6.15
Cu 10.9 10.27 94.22 5.78 10.9 10.38 95.23 4.77 10.9 10.48 96.15 3.85
Pb 0.5 0.04 8.00 92.00 0.5 0.045 9.00 91.00 0.5 0.053 10.60 89.40
Zn 46 28.21 61.33 38.67 46 32.16 69.91 30.09 46 34.2 74.35 25.65
Mo 17 15.35 90.29 9.71 17 15.93 93.71 6.29 17 16 94.12 5.88
PVA-1
Cd 2.81 1.98 70.46 29.54 2.81 2 71.17 28.83 2.81 2.1 74.73 25.27
Cr 52 41.6 80.00 20.00 52 44.57 85.71 14.29 52 45.76 88.00 12.00
Cu 10.9 9.79 89.82 10.18 10.9 10.2 93.58 6.42 10.9 10.28 94.31 5.69
Pb 0.5 0.035 7.00 93.00 0.5 0.041 8.20 91.80 0.5 0.043 8.60 91.40
Zn 46 25.1 54.57 45.43 46 28.45 61.85 38.15 46 30.63 66.59 33.41
Mo 17 13.87 81.59 18.41 17 14.45 85.00 15.00 17 15.11 88.88 11.12
PVA-2
Cd 2.81 2.03 72.24 27.76 2.81 2.29 81.49 18.51 2.81 2.31 82.21 17.79
Cr 52 45 86.54 13.46 52 46.43 89.29 10.71 52 47.43 91.21 8.79
Cu 10.9 10.21 93.67 6.33 10.9 10.26 94.13 5.87 10.9 10.38 95.23 4.77
Pb 0.5 0.038 7.60 92.40 0.5 0.046 9.20 90.80 0.5 0.05 10.00 90.00
Zn 46 25.73 55.93 44.07 46 28.7 62.39 37.61 46 36.21 78.72 21.28
Mo 17 15.62 91.88 8.12 17 15.77 92.76 7.24 17 15.89 93.47 6.53

Abbreviation: T = total, CX = extraction, L = leached (%L) = (CxCd/TCd) * 100%, M = mobility (%M) = (TCd–CxCd/TCd) * 100%.

3.1.1

3.1.1 Cadmium

The maximum percentage removal of cadmium was found to be 65%, 69%, 75% and 82% from original Cd present in PEG-1, PEG-2, PVA-1, and PVA-2, respectively, indicating that the removal of Cd increased with increased polymer MW and dosage. That is to say, PEG mobility and PVA mobility would be improved with PEG and PVA molecular weight increasing. So an increment in PEG and PVA molecular weight had two contrary effects on PEG mobility and PVA mobility. This is because higher MW and dosage of adsorbent increase the surface area, thereby increasing the greater availability of exchangeable sites for the metal ions to get adsorbed. It can be concluded that the cadmium ions are then electrostatically attracted to the high electron density regions of the functional groups and form coordination bonds to the polymer. Due to its strong di positive charge, it often forms coordinating bonds between multiple functional groups within PEG and PVA polymers. Accordingly, the amounts of Cd in the PEG-1, PEG-2, PVA-1, and PVA-2 may be remobilized from treated PG to the ecosystem which are 35%, 31%, 25%, and 18%, respectively. However, the removal of cadmium with different polymers followed the order: PEG-1 > PEG-2 > PVA-1 > PVA-2. To further assess the mobility of the analyzed heavy metals, correlation coefficients (r) were used as a measure of the degree of mobility as shown in Table 2. The good correlation between the total Cd content and the amount of Cd leached by PEG and PVA is (r = 0.59 and r = −0.63, respectively), shown in Fig. 2. It is evident that Cd is intermediate mobility, indicating Cd (<35) is going to be leached from treated PG into environment (Table 2).

Table 2 Degree of element mobility based on PEG and PVA leaching method for the phosphogypsum samples.
Variable Reagent (r) values Degree of mobility Overall assessment
Cd PEG 0.59c Intermediate Intermediate
PVA 0.63c Intermediate
Cr PEG 0.90d High High
PVA 0.84d High
Cu PEG 0.98d High High
PVA 0.84d High
Pb PEG 0.32b low Low
PVA 0.64c Intermediate
Zn PEG 0.97d High Intermediate
PVA 0.53c Intermediate
Mo PEG 0.74c Intermediate High
PVA 0.93d High

a Very low mobility (r = 0–0.25).

b Low mobility (r = 0.26–0.50).
c Intermediate mobility (r = 0.51–0.75).
d High mobility (r = 0.76–1.00).
Relationship between the total Cd, Cr, and Cu content and their metal extract using PEG and PVA polymer.
Figure 2 Relationship between the total Cd, Cr, and Cu content and their metal extract using PEG and PVA polymer.

3.1.2

3.1.2 Chrome

The maximum percentage removal of chrome was found to be 87%, 94%, 88% and 91% from original Cr present in PEG-1, PEG-2, PVA-1, and PVA-2, respectively, indicating that the removal of Cr increased with increased polymer MW and dosage. Accordingly, the amounts of Cr may be remobilized from treated PG to the ecosystem which are 13%, 6%, 12%, and 9%, respectively.

However, the removal of Cr with different polymers followed the order: PEG-1 > PVA-1 > PVA-2 > PEG-2. The high positively significant correlation between the total Cr content and the amount of Cr leached by PEG and PVA is (r = 0.90 and r = 0.84, respectively), shown in Fig. 2. It is evident that Cr has high mobility, indicating Cr (<13) is going to be leached from treated PG into environment (Table 2).

3.1.3

3.1.3 Copper

The maximum percentage removal of copper was found to be 96%, 96%, 94% and 95% from original Cu present in PEG-1, PEG-2, PVA-1, and PVA-2, respectively, indicating that the removal of Cu increased with increased polymer MW and dosage. Accordingly, the amounts of Cu may be remobilized from treated PG to the ecosystem which are 4%, 4%, 6%, and 5%, respectively.

However, the removal of Cu with different polymers followed the order: PVA-1 > PVA-2 > PEG-1 = PEG-2. The high positively significant correlation between the total Cu content and the amount of Cu leached by PEG and PVA is (r = 0.98 and r = 0.84, respectively), shown in Fig. 2. It is evident that Cu has high mobility, indicating Cu (<6) is going to be leached from treated PG into environment (Table 2).

3.1.4

3.1.4 Lead

The maximum percentage removal of Pb was found to be 10%, 11%, 9% and 10% from original Pb present in PG of PEG-1, PEG-2, PVA-1, and PVA-2, respectively (Table 1), indicating the high percentage of lead in the four adsorbents indicated that Pb present in different mineral surfaces varied considerably. It was high probably due to weak specific (covalent) interaction of Pb with organic matter and other surfaces (Zimdahl and Skogerboe, 1997). Accordingly, the amounts of Pb may be remobilized from treated PG to the ecosystem which are 96%, 96%, 94%, and 95%, respectively. However, the removal of Pb with different polymers followed the order: PVA-1 > PVA-2 > PEG-1 = PEG-2. The low negatively significant correlation between the total Pb content and the amount of Pb leached by PEG is r = −0.32 and good positively significant correlation between the total Pb content and the amount of Pb leached by PVA is r = 0.64, shown in Fig. 3. It is evident that Pb (<96%) has low to intermediate mobility, indicating Pb (<96) is going to be leached from treated PG into environment (Table 2).

Relationship between the total Pb, Zn and Mo content and their metal extract using PEG and PVA polymer.
Figure 3 Relationship between the total Pb, Zn and Mo content and their metal extract using PEG and PVA polymer.

3.1.5

3.1.5 Zinc

The maximum percentage removal of Zn was found to be 68%, 74%, 67% and 79% from original Zn present in PG of PEG-1, PEG-2, PVA-1, and PVA-2, respectively (Table 1), indicating that most of the Zn accommodating in different mineral phases in PG, may be because it was associated with Fe-oxides in the PG lattice structures (Nathan et al., 1997). A sizably greater presence of Zn was also seen in the organic phase. Zinc as a substitute for Ca, entering the gypsum crystal has also been widely recognized (Altschuler, 1980). Accordingly, the amounts of Zn may be remobilized from treated PG to the ecosystem which are 32%, 26%, 33%, and 21%, respectively. The removal of Zn with different adsorbents followed the order: PVA-1 > PEG-1 > PEG-2 > PVA-2. The high positively significant correlation between the total Zn content and the amount of Zn leached by PEG and PVA is (r = 0.98 and r = 0.53, respectively), shown in Fig. 3. It is evident that Zn has high mobility, indicating Zn (<33) is going to be leached from treated PG into environment (Table 2).

3.1.6

3.1.6 Molybdenum

The maximum percentage removal of Mo was found to be 86%, 94%, 89% and 93% from original Mo present in PEG-1, PEG-2, PVA-1, and PVA-2, respectively (Table 1), indicating that the removal of Mo increased with increased polymer MW and dosage. Accordingly, the amounts of Mo may be remobilized from treated PG to the ecosystem are 14%, 6%, 11%, and 7%, respectively. However, the removal of Mo with different polymers followed the order: PVA-1 > PEG-1 > PVA-2 > PEG-2. The high positively significant correlation between the total Mo content and the amount of Mo leached by PEG and PVA is (r = 0.74 and r = 0.94, respectively), shown in Fig. 3. It is evident that Mo has high mobility, indicating Mo (<14) is going to be leached from treated PG into environment (Table 2).

3.2

3.2 Ecological risk assessment

Table 3 summarizes the potential ecological risk factors (Eri) and risk indices (RI) for Cd, Cr, Cu, Pb, and Zn values in untreated PG samples and treated PG samples. It was found that Eri values in the untreated Cd were 84, indicating considerable potential ecological risk, while Cd values in the treated PG were below 80, indicating moderate potential ecological risk (Fig. 4). The values (Eri) of Cr, Cu, Pb, and Zn in untreated PG samples and treated PG samples were below 40, which indicate that all investigated heavy metals except Cd posed no potential hazard to the ecosystem (Fig. 4). The rank of risk contribution rate (Eri/RI) among the heavy metals in a descending order is Cd > Zn > Cu > Cr > Pb. Thus, Cd made the largest contribution to the total risk index while Pb made the smallest contribution. Since Cd is more highlighted than other elements in terms of the ecological risk factor in the PG, it should be paid special attention to. The order of the potential risk indices (RI) for the four polymers is PVA-2 > PVA-1 > PEG-2 > PEG-1. The risk level of PVA-2, PVA-1, PEG-2 and PEG-1 was low degree. The result can be explained by the fact that the PVA-2 extract was higher than PVA-1 and PEG-2 in the PG, while the PEG-1 extract in the PG is lowest. The calculated integrated potential ecological risk indices (RI = ∑Eri) considered that Cd, Cr, Cu, Pb, and Zn indicated pollution in all studied samples is less.

Table 3 The potential ecological risk factors and risk indices of metals based on different polymers dosages in phosphogypsum.
Reagent Dosage Eri RI Degree
Cd Cr Cu Pb Zn
PG – 84.3a 1.16 1.09 0.04 0.26 86.85 Low
PEG-1 0.5 47.7 0.95 1.02 0.003 0.160 49.83 Low
0.7 51.0 0.97 1.03 0.003 0.175 53.18 Low
1.0 54.6 1.00 1.05 0.004 0.180 56.83 Low
PEG-2 0.5 55.5 1.08 1.03 0.003 0.160 57.78 Low
0.7 56.7 1.05 1.04 0.003 0.184 58.98 Low
1.0 58.5 1.08 1.05 0.004 0.200 60.83 Low
PVA-1 0.5 59.4 0.92 0.98 0.003 0.140 61.45 Low
0.7 60.0 0.99 1.02 0.003 0.163 62.18 Low
1.0 63.0 1.02 1.03 0.003 0.180 65.22 Low
PVA-2 0.5 60.9 1.00 1.02 0.003 0.150 63.07 Low
0.7 68.7 1.03 1.03 0.003 0.164 70.92 Low
1.0 69.3 1.05 1.04 0.004 0.210 71.60 Low

bConsiderable risk.

cHigh risk.

dVery high risk.

a Moderate risk.
Ecological risk assessment of heavy metals.
Figure 4 Ecological risk assessment of heavy metals.

4

4 Conclusion

The results of the present work suggested that the addition of PEG and PVA with different molecular weights could change the PG structure and properties to remove heavy metals. During batch experiments, because of the addition of PEG and PVA with increasing molecular weight and with increasing dosage, a decrease in mobility increases the heavy metals removal. The results of heavy metal removal from PG leachate with polymer methods consisting of PEG and PVA were approved. The batch experiments’ result obtained showed that the removal of Cd, Cr, Cu, Pb, Zn and Mo in these samples ranged from 57% to 70%, 80% to 94%, 90% to 96%, 7% to 11%, 55% to 74%, and 81% to 94%, respectively for PEG, and from 70% to 84%, 80% to 91%, 89% to 95%, 7% to 10%, 55% to 78%, and 82% to 93%, respectively for PVA. The potential ecological risk factors (Eri) showed that Cd should be considered a moderate potential ecological risk, whereas Cr, Cu, Pb, and Zn indicated a low ecological risk. The potential ecological risk indices (RI) considered that Cd, Cr, Cu, Pb, and Zn indicated pollution in all studied samples is less. These results indicated that Cd, Cr, Cu, Pb, and Zn content removal using PEG and PVA polymers would be of great importance in environmental applications, and they can be considered a very suitable safe use of PG in agriculture and soil amendment.

Acknowledgments

The authors would like to thank the Jordan Phosphate Mines for XRF analyses. The authors are also grateful to Ibin Hayan Laboratory (Aqaba) for AAS analyses. The author is thankful to Mr Christiaan H. Van Niekerk, lecturer in English language, King Saud University-Muzahimiyah Branch for improvement of the English language of this manuscript.

References

  1. , , , . Bioavailability and mobility of trace metals in phosphogypsum from Aqaba and Eshidiya, Jordan. Chemie der Erde Geoch.. 2010;70:283-291.
    [Google Scholar]
  2. , , , , . Selectivity assessments of a sequential extraction procedure for potentially trace metals mobility and bioavailability in phosphate rocks from Jordan Phosphate Mines. Soil Sediment Contam.. 2013;23:417-436.
    [Google Scholar]
  3. , . Sulfoaluminate-belit cement from limestone, phophogypsum and other waste product. Stud., Technol.. 2004;12:928-935.
    [Google Scholar]
  4. , , , . Effects of enhanced UV-B on growth and yield of two Syrian crops wheat (Triticum durum var. Horani) and broad beans (Vicia faba) under field conditions. Environ. Exp. Bot.. 1998;40:11-16.
    [Google Scholar]
  5. , . The geochemistry of trace elements in marine phosphorites, Part I: characteristic abundances and enrichment. SEPM Spec. Publ.. 1980;29:19-30.
    [Google Scholar]
  6. , , . Studies on chromium (VI) adsorption–desorption using immobilized fungal biomass. Bioresour. Technol.. 2003;87(1):17-26.
    [Google Scholar]
  7. , , , . Assessing heavy metal contamination in Sado Estuary sediment: an index analysis approach. Ecol. Ind.. 2005;5:151-169.
    [Google Scholar]
  8. Carmichael, J.B., 1988. Worldwide production and utilization of PG. In: Proceedings of the Second International Symposium on PG. Miami, Florida, U.S.A. Florida Institute of Phosphate Research Publication, 05-037-055.
  9. , , , . Acid activation and bleaching capacity of bentonites from the islands of Milos and Chios, Aegean, Greece. Appl. Clay Sci.. 1997;12(4):329-347.
    [Google Scholar]
  10. , , , , . Selective removal of the heavy metal ions from waters and industrial waste waters by ion-exchange method. Chemosphere. 2004;56:91-106.
    [Google Scholar]
  11. , , , , , , , . PG amendment effect on radionuclide content in drainage water and marsh soils from southwestern Spain. Environ. Qual.. 2003;32:1262-1268.
    [Google Scholar]
  12. , . Removal of arsenic in water using polypyrrole and its composites. World Appl. Sci.. 2008;3(1):10-13.
    [Google Scholar]
  13. , . Removal of chromium from waste water using polyaniline. J. Appl. Polym. Sci.. 2007;104:1964-1967.
    [Google Scholar]
  14. , , . Waste gypsum from intermediate dye industries for production of building materials. Constr. Build. Mater.. 2010;24:1632-1637.
    [Google Scholar]
  15. , . An ecological risk index for aquatic pollution control: a sedimentological approach. Water Res.. 1980;14:975-1001.
    [Google Scholar]
  16. , , , . Sotpotion of copper (II) and nickel (II) ions to on chitin/polyvinyl alcohol binary blend: kinetics and equilibrium studies. Int. J. Environ.. 2011;2(2):624-637.
    [Google Scholar]
  17. , , , , , . Acta Cryst.. 2003;C59:0703-0705.
  18. , , , , . Immobilization of enzyme into poly(vinyl alcohol) membrane. Biotechnol. Bioeng.. 1986;28:1721-1726.
    [Google Scholar]
  19. ISO 11466, 1995. Soil quality-extraction of trace elements soluble in aqua regia. International Organization for Standardization Case Postale 56 l CH-l 211 Geneve 20 Switzerland, <http://www.iso.org/iso/catalogue_detail.htm?csnumber=19418>.
  20. , , , , . Reduction of clinkerization temperature by using PG. J. Hazard. Mat.. 2006;B137:129-137.
    [Google Scholar]
  21. , , , . Remediation modelling and preconcentration of Cd (II) ions in aqueous media using polymer assisted ultrafiltration A green analytical approach. ChemXpress. 2012;1(1):10-15.
    [Google Scholar]
  22. , , . Radiation-grafted copolymers for separation and purification purposes: status, challenges and future directions. Progr. Polym. Sci.. 2012;37:1597-1656.
    [Google Scholar]
  23. , , , , , . Geochemistry of cadmium in the Negev phosphorites. Chem. Geol.. 1997;142:87-107.
    [Google Scholar]
  24. , , , , . The application of PG in agriculture and the radiological impact. J. Environ. Rad.. 2006;89:188-198.
    [Google Scholar]
  25. , , , . Influence of Portland cement type on unconfined compressive strength and linear expansion of cement-stabilized PG. J. Environ. Eng.. 2003;129:956-960.
    [Google Scholar]
  26. , , , , . An investigation into the effect of various chemical and physical treatments of a South African PG to render a suitable as a set retarder for cement. Cem. Concr. Res.. 2003;33:1223-1227.
    [Google Scholar]
  27. , , , . Poly(N-acetyl-α-acrylic acid). Synthesis, characterization and chelation properties through liquid-phase polymer-based retention (LPR) technique. Macromol. Rapid Comm.. 2001;22:418-422.
    [Google Scholar]
  28. , , , . Heterogeneous distribution of radionuclides, barium and strontium in PG by-product. Sci. Total Environ.. 1996;180:201-209.
    [Google Scholar]
  29. , , , . Removal of hexavalent chromium using distillery sludge. Bioresour. Technol.. 1997;89:207-211.
    [Google Scholar]
  30. , , , , , . An improved process for the purification of PG. Constr. Build. Mater.. 1996;10(8):597-600.
    [Google Scholar]
  31. , . Influence of PG impurities on two properties of Portland cement. Indian Concr.. 1987;61:186-190.
    [Google Scholar]
  32. , . Influence of thermally treated phophogypsum on the properties of Portland slag cement. Resour. Conservat. Recycl.. 2007;52:28-38.
    [Google Scholar]
  33. , , , , , . Environmental impact and management of phophogypsum. J. Environ. Manag.. 2009;90:2377-2386.
    [Google Scholar]
  34. , , . Purification of South African PG for use as Portland cement retarder by a combined thermal and sulphuric acid treatment method. South African J. Sci.. 2004;100:411-414.
    [Google Scholar]
  35. , , , , . Calculation of heavy metals’ toxicity coefficient in the evaluation of potential ecological risk index. Environ. Sci. Tech.. 2008;31:112-115.
    [Google Scholar]
  36. , , , . Removal of some heavy metals from their aqueous solutions using 2 acrylamido-2-methyl-1-propane sulfonic acid/polyvinyl alcohol copolymer hydrogels prepared by gamma irradiation. Arab J. Nucl. Sci. Appl.. 2013;46(2):80-91.
    [Google Scholar]
  37. , , , . Adsorptive capacities of activated carbon for organic constituents of waste waters. Environ. Prog.. 1990;9(1):1-9.
    [Google Scholar]
  38. , , . Removal of metals and other cations from water using zeolites. Sep. Sci. Technol.. 1992;27(14):1969-1984.
    [Google Scholar]
  39. , , . Behavior of lead in soil. Environ. Sci. Technol.. 1977;11:1202-1207.
    [Google Scholar]

Fulltext Views
840

PDF downloads
244
View/Download PDF
Download Citations
BibTeX
RIS
Show Sections

Suggested read for related articles: