IEEE Proof IEEE TRANSACTIONS ON NUCLEAR SCIENCE 1 Red Mud Characterization Using Atomic and Nuclear Analytical Techniques Jasmina Obhodas, Davorin Sudac, Lidija Matjacic, and Vladivoj Valkovic Abstract—Red mud is a toxic waste left as a byproduct in aluminum production Bayer process. Since it contains significant concentrations of other chemical elements interesting for industry, including Rare Earths Elements (REEs), it is also potential sec- ondary ore source. Recent events in some countries have shown that red mud presents a serious environmental hazard if not properly stored. The subject of our study is evaluation of the red mud elemental composition, especially yttrium, scandium, gallium and REEs, from an ex-aluminum plant in Obrovac, Croatia, left from the processing of bauxite mined during late 70’s and early 80’s at the eastern Adriatic coast and stored in open concrete basins for more than 30 years since then. We have used energy dispersive x-ray fluorescence analysis (both tube and radioactive source excitation), fast neutron ac- tivation analysis and passive gamma spectrometry to identify a number of elements present in the red mud, their concentration levels and radioactivity in the red mud. The high concentrations of Al, Si, Ca, Ti and Fe have been measured. Chemical elements Sc, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Br, Y, Rb, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pb, Th and U were found in lower concentrations. No significant levels of radioactivity have been measured. Index Terms—[Author, please supply index terms/keywords for your paper. To download the IEEE Taxonomy go to http://www.ieee. org/documents/2009Taxonomy_v101.pdf.]. I. INTRODUCTION R ED Mud (RM) represent the poorly soluble part of the bauxite remained after the alkaline extraction of by the Bayer procedure. The red color is generally from iron ox- ides, which are dominant in its composition. In addition, red mud can contain a number of chemical elements which today play a prominent role as strategic elements for development of high-tech, renewable-energy, and defense-related technologies. Today’s list of these critical elements would likely include most of the REEs along with scandium, yttrium and gallium which are commonly found in RM enriched 10–20 folds over normal concentrations in the earth crust. Manuscript received December 08, 2011; revised June 15, 2012; accepted June 18, 2012. This work was supported in part by the EU FP7 Project No. 218148, UNCOSS—Underwater Coastal Sea Surveyor. J. Obhodas is with the Department of Experimental Physics, Institute Ruder Boskovic, Zagreb, Croatia (e-mail: jobhodas@irb.hr). D. Sudac and L. Matjacic are with the Department of Experimental Physics, Institute Ruder Boskovic, Zagreb, Croatia (e-mail: dsudac@irb.hr; Lidija.Mat- jacic@irb.hr). V. Valkovic is with the A.C.T.d.o.o., Prilesje 4, Zagreb, Croatia (e-mail: vlado@act-doo.hr). Digital Object Identifier 10.1109/TNS.2012.2206608 In this work we present the results of the measurements of the composition of REE and other elements in the red mud left after the closure of the aluminum processing plant in Croatia, 30 years ago. The plant was shut down in 1981 after three years of operation owing to some political and economic factors. The plant was producing 300,000 tons of alumina per year, resulting in about of RM and of waste base (WB) remained to this day in two concrete basins as it is shown in Fig. 1. Improperly managed red mud disposals can have serious con- sequences for the environment and security of people. Concerns about toxicity should be paid more to WB because of its high pH value, although the red mud itself can physically cause a lot of damage if it suddenly burst out of the reservoirs. Unfortunately, such case happened in October 2010 in Kolontar red mud dis- posal in Hungary, when 9 people died from drowning and 40 people suffered mostly from chemical burns caused by the WB [1]. In this paper we discuss RM as a possible secondary raw material for yttrium, scandium, gallium and REEs production based on the results of our measurements. In addition we pro- pose a biological remediation of WB by using Spirulina spp bac- teria. II. MATERIALS AND METHODS Analysis of RM was done on samples prepared from 5 kg of composite sample, collected from both basins in previous survey [2]. Prior to analysis RM was dried in oven at overnight, sieved to a fraction size of 0.7 mm, grinded and ho- mogenized. REEs were analyzed by the energy dispersive x-ray fluorescence technique (EDXRF) by using Bq ring-shaped Am radioactive source for irradiation of 2 g pellets, 2.5 cm in diameter and pressed under 9 t. Samples were placed in 99.9% grade aluminum holder 12 mm distant from the source. The ir- radiation time was 3000 s. X-ray spectra were collected with a Canberra Ge(Li) detector (GL0055P, FWHM 155 eV at 5.9 keV). lines were fitted by using AXIL program from the QXAS software package [3]. Acquisition system was made at Ruder Boskovic Institute. Standard addition method was used for a quantitative analysis of REEs. After addition of the dif- ferent amounts of a standard (see Fig. 4), samples were mixed for 15 minutes in a mixer (5100 Mixer/Mill SPEX SamplePrep LLC) prior to each analysis and then pressed into pellets. Every sample was analyzed two times. As the standard reference ma- terials (SRMs) 99.9% grade REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm) obtained from the Metall Rare Earth Ltd, Shenzhen, China were used. For La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy emission lines were analyzed. Elements Ho, Er 0018-9499/$31.00 © 2012 IEEE