Geothermics 50 (2014) 30–34 Contents lists available at ScienceDirect Geothermics journal homepage: www.elsevier.com/locate/geothermics Adsorption applications of unmodified geothermal silica Halldor G. Svavarsson a,b,∗ , Sigurbjorn Einarsson a , Asa Brynjolfsdottir a a Blue Lagoon Ltd., Iceland b School of Science and Engineering, Reykjavík University, Iceland article info Article history: Received 22 February 2013 Received in revised form 16 July 2013 Accepted 1 August 2013 Available online 6 September 2013 Keywords: Geothermal silica Chromatographic Adsorption Protein separation Phycocyanin abstract Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporat- ing the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amor- phous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Geothermal silica Geothermal resources are widespread throughout the world although generally associated with areas of volcanic activity. The HS-Energy geothermal powerplant is located in Svartsengi on the Reykjanes peninsula, south–west Iceland on a sequence of lava flows, the youngest being roughly 800 years old (Saemundsson et al., 2010). The geological structure is further characterised by interlayers of scoria and hyaloclastite reflecting interglacial and glacial periods. Since the lava flows, scoria and interlayers of hyalo- clastite are highly porous and permeable, they allow seawater to percolate deep into their aquifers where it heats up and mixes with meteoric water (Arnorsson, 1995). Geothermal wells drilled through the lava flows to depths of up to 2000 m discharge a mix- ture (here referred to as geothermal fluid) of 2/3 seawater and 1/3 meteoric water with a temperature of about 240 ◦ C. Due to leaching the hot geothermal fluid contains a high concentration of silicon (Si) when it enters the wells. Originally, the silicon is present in the hot geothermal fluid as silicic acid (SiO x (OH) 4–2x ) n . Upon cool- ing, the silicic acid precipitates as a three-dimensional network of coagulated primary silica (SiO 2 ) particles. The primary particles grow up to some nanometers in size before they coagulate to form aggregated clusters. Such a small particle size gives rise to high ∗ Corresponding author. Tel.: +354 5996200; fax: +354 5996201. E-mail address: halldorsv@ru.is (H.G. Svavarsson). specific surface area, which makes the SiO 2 a suitable candidate for adsorption and catalytic applications. Steam from the flashed geothermal fluid is used to produce electricity (output power of ∼75 MW e ). The residual liquid is used in a heat exchange process (output power of ∼150 MW t ) to heat up freshwater for district heating of local communities of roughly 20,000 habitants. This heat exchange process limits the mini- mum temperature for heat extraction of the geothermal fluid to about 90 ◦ C. Most of the spent geothermal fluid is reinjected into the geothermal reservoir (∼6 × 10 6 m 3 annually) but some of it (∼1.2 × 10 6 m 3 annually) is discharged on the surface where it forms the Blue Lagoon (Grether-Beck et al., 2008; Petursdottir et al., 2009). A small fraction of the discharged fluid is bypassed to sed- imentation tanks at the Blue Lagoon where it cools from 90 ◦ C to ambient temperature. The cooling causes supersaturation of the silicic acid which in turn precipitates as amorphous SiO 2 . The pH of the resulting supernatant is 7.7 ± 0.2, sligthly higher than the pH of the Blue Lagoon which is 7.5 ± 0.2. At 90 ◦ C, the geothermal fluid contains about 600 ppm SiO 2 and thus the 7 × 10 6 m 3 of liq- uid being discharged and reinjected annually carries about 4000 tonnes. At 10–15 ◦ C, a realistic ambient temperature, the SiO 2 con- centration has dropped by roughly an order of magnitude (Fleming and Crerar, 1982) and thus a precipitation of over 3000 tonnes could potentially be harnessed annually from fluid discharged from the HS-Energy facility alone. Few authors have reported on practical applications of modi- fied geothermal SiO 2 and still fewer on applications of unmodified SiO 2 . A possible use of geothermal SiO 2 as a filler in paper (Johnston et al., 2004) and as a precursor for silicates (Gallup et al., 2003) has 0375-6505/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.geothermics.2013.08.001