ARTICLE pubs.acs.org/est
Uptake of Sr2+ and Co2+ into Biogenic Hydroxyapatite: Implications for Biomineral Ion Exchange Synthesis Handley-Sidhu S.,†,* Renshaw J. C.,† Moriyama S.,|| Stolpe B.,† Mennan C.,‡ Bagheriasl S.,§ Yong P.,‡ Stamboulis A.,§ Paterson-Beedle M.,‡ Sasaki K.,|| Pattrick R. A. D.,^ Lead J. R.,† and Macaskie L. E.‡ School of Geography Earth and Environmental Sciences, ‡School of Biosciences, §School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K. Department of Earth Resource Engineering, Kyushu University, Fukuoka, 819-0395, Japan. ^ School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.
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bS Supporting Information ABSTRACT: Biomineral hydroxyapatite (Bio-HAp) produced by Serratia sp. has the potential to be a suitable material for the remediation of metal contaminated waters and as a radionuclide waste storage material. Varying the Bio-HAp manufacturing method was found to influence hydroxyapatite (HAp) properties and consequently the uptake of Sr2+ and Co2+. All the BioHAp tested in this study were more efficient than the commercially available hydroxyapatite (Com-HAp) for Sr2+ and Co2+ uptake. For Bio-HAp the uptake for Sr2+ and Co2+ ranged from 24 to 39 and 29 to 78 mmol per 100 g, respectively. Whereas, the uptake of Sr2+ and Co2+ by Com-HAp ranged from 3 to 11 and 4 to 18 mmol per 100 g, respectively. Properties that increased metal uptake were smaller crystallite size (70 m2 g1). Organic content which influences the structure (e.g., crystallite arrangement, size and surface area) and composition of Bio-HAp was also found to be important in Sr2+ and Co2+ uptake. Overall, Bio-HAp shows promise for the remediation of aqueous metal waste especially since Bio-HAp can be synthesized for optimal metal uptake properties.
’ INTRODUCTION Current technologies for the removal of radionuclides from nuclear waste waters include osmosis, ultrafiltration and precipitation1 but these are often expensive and require high maintenance. Another approach is to use a sorbent or ion exchange material that can be disposed of once its full capacity is reached.2 Natural ion exchangers such as clay minerals, vermiculite and clinoptilolite have largely been replaced due to their low exchange capacities and inconsistent quality.2 Standard practice in the nuclear industry is to use costly specialist synthetic ion exchangers such as titanates, zeolites, and hexacyanoferrates.2 Recently, members of the apatite group (general formula Ca5(PO4)3(OH,F,Cl)) which have ion exchange capacity, have been assessed for the remediation of heavy metals in groundwater3 and as a potential nuclear waste disposal material.4 Apatites are suitable materials for waste storage because they incorporate actinides in their structure, are stable over long time periods and are resistant to self-radiation.4 Biogenic phosphate minerals such as hydroxyapatite (Ca10(PO4)6(OH)2),5 uranyl hydrogen phosphate (UO2HPO4 3 3H2O)6 and zirconium phosphate (Zr(HPO4)2 3 nH2O)7 are also promising materials because they can sorb a range of metals, with an uptake capacity higher than some commercially available materials. r 2011 American Chemical Society
Serratia sp. cells biomanufacture nanophase hydroxyapatite (Bio-HAp) from glycerol 2-phosphate (G2P) and Ca2+.8 Serratia sp. contains high levels of an atypical phosphatase enzyme located in the bacterial periplasmic space and attached to extracellular polymeric substance (EPS); this enzyme cleaves G2P, liberating inorganic phosphate and providing the nucleation site for the growth of calcium phosphate crystals.8 Biomineralization and the growth of hydroxyapatite crystals is controlled within spatial localization of the biological space on and in close proximity to cells. Hydroxyapatite crystal size and morphology can be controlled by manipulating the solution chemistry (i.e., inorganic species concentrations and pH) and by stressing the organism using different growth media and pH. In this study we investigated the efficacy of differently prepared hydroxyapatite biominerals for the uptake of Sr2+ and Co2+; 90Sr and 60 Co are major contributors to radioactivity in nuclear wastes and contamination. The objectives of this study were to (1) fully characterize the properties of the various biomanufactured hydroxyapatite (2) evaluate the relationship between these properties and Received: May 3, 2011 Accepted: June 29, 2011 Revised: June 28, 2011 Published: June 29, 2011 6985
dx.doi.org/10.1021/es2015132 | Environ. Sci. Technol. 2011, 45, 6985–6990
Environmental Science & Technology
ARTICLE
Table 1. Showing the Changes to the Base Protocol for Bio-HAp 1-9B sample
notes
Ca2+ (mM)
G2P (mM)
citrate (mM)
pH
refs 5
base protocol Bio-HAp (1)
daily dose, 8 days
1
5
2
9.2
Bio-HAp (2)
daily dose, 5 days
1
5
0
9.2
Bio-HAp (3)
total initial dose, reaction time of 5 days
10
25
10
9.2
Bio-HAp (4)
continuous column fed, 11 days
10
25
20
9.2
Bio-HAp (5)
daily dose, 8 days
2
5
0
7.2
Bio-HAp (6)
daily dose, 8 days
2
5
2
7.2
Bio-HAp (7)
daily dose, 8 days
2
5
0
9.2
Bio-HAp (8) Bio-HAp (9A)
daily dose, 8 days daily dose, 5 days. PHB extracted.
2 2
5 10
2 4
9.2 9.2
Bio-HAp (9B)
daily dose, 5 days. PHB extracted.
2
10
4
9.2
metal uptake and (3) determine the optimal bio-HAp production protocol for metal remediation.
’ MATERIALS AND METHODS Hydroxyapatite Material. The production of Bio-HAp by Serratia sp. (NCIMB 40259 used by kind permission of Isis Innovation, Oxford, UK) has been described in detail elsewhere5 and variations of this base method (Bio-HAp 19) are shown in Table 1. Serratia sp. is novel because it produces both HAp and polyhydroxy-β-butyrate (PHB) from G2P and Ca2+.9 For replicate samples Bio-HAp (9A) and (9B), the PHB was removed from the precipitate after biomineral formation by using a chloroform method.9 Following preparations of the Bio-HAp on the cells (Table 1) the biominerals formed were washed in water, then acetone, air-dried and stored at room temperature until use (
