Characterization and valorisation of norm wastes: application to the tio2 production industry

1st Spanish National Conference on Advances in Materials Recycling and Eco – Energy Madrid, 12-13 November 2009 S03-3 79 CHARACTERIZATION AND VALORISATION OF NORM WASTES; APPLICATION TO THE TIO2 PRODUCTION INDUSTRY M.J. Gázquez1*, J. Mantero2, J.P. Bolívar1, R García-Tenorio2 and F. Galán1 1 Department of Applied Physics, University of Huelva 21071, Huelva, Spain 2 Department of Applied Physics II, University of Seville, Spain *Corresponding author. Tel.: +34 959 219798; E-mail addresses: [email protected] Abstract The present study was focused to characterize the raw materials, wastes and several co-products from titanium dioxide industry, in particular their elemental composition (major, minor and trace elements), mineralogy, and radioactive contents, with the objective to apply this knowledge to valorize these materials in fields such as construction, civil engineering, fertilizers manufacturing, etc. Keywords: Ilmenite, red gypsum, waste, valorisation, titanium dioxide. INTRODUCTION The recycling of waste material generated in the majority of industrial production processes is the subject nowadays of more and more research for several reasons. The protection of health and the environment are of great importance, although the economic benefits accruing from waste recycling cannot be neglected either [1–2]. The minimization of waste disposal, avoiding its direct release into the environment, generates not only health and environmental benefits in several industrial processes, in addition to the generation of the main product; the appropriate treatment of a fraction of the waste generated could lead to the production of co-products with economic value and broad applications [3]. There is a paradigmatic NORM industry (NORM = Naturally Occurring Radioactive Material) hat applies widely the recycling strategy. It is located in the province of Huelva and produces titanium dioxide pigments, and two different co-products obtained as a consequence of the treatment of waste generated throughout the process. Two raw materials are used as feedstock in titanium dioxide production at the Huelva factory: ilmenite (FeTiO3) and slag. Ilmenite is a heavy mineral containing approximately 43–65 % titanium dioxide [4], and can be considered as a NORM material because generally contains enhanced amounts of uranium and thorium depending deeply from this geological origin. The titaniferous slag, which contains 70–80 % in titanium dioxide, is a co-product resulting of the smelting of ilmenite [5]. The oldest and most common process for titanium dioxide production is the sulphate process (see Fig 1), being its main steps the followings: 1. Digestion of the ore (batch operation): A carefully controlled blend of illmenite and slag is mixed with highly concentrated sulphuric acid (80–95 %) to digest the TiO2 containing feedstock. The resulting liquor contains titanyl sulphate (TiOSO4) and iron sulphate (FeSO4) dissolved in sulphuric acid. To ensure that all the Fe is in dissolution, the liquor is passed through a bath of scrap metal (Fe reduction step). 2. Clarification of the resulting liquor: The reduced liquor flows into a clarification tank where the un-dissolved solids (mud) are separated from the solution by flocculation and filtration. 3. Titanium dioxide precipitation: The clarified liquor is then hydrolyzed in order 1st S Figure 1. Dia g to produce t 4. H TiO 2 after mother liq u filters”).Thi s by-product, co-product s 5. T mother liqu o water in or d The g ener a wash can b process. 6. T for the rem o sulphur. Th e washed, d before be it Init i liquor ( “stro a batch c removed a (FeSO 4 ·7H 2 of the TiO 2 ( CAP ) . T h re-concentr step, bein g sulphate m co-product resultin g cl e introduced i On coming fro m processed S panish Nat g ram of the sul p t he precipita t Hy drated Ti O its precipita t u or b y vac u s liquor c and it is tre a s , as will be d T iO 2 washin g o r, the filter e d er to remo v a ted weak a c b e considere d T he TiO 2 pul p o val its wate r e resultin g s o ried and fi n packed for c i all y , the firs t n g ” acid, 20 – ooler cr y st a a s solid fer r 2 O). This co process, co h e remaini n ated for its g precipitat e m onoh y drate that is sepa e an sulphuri c i n the illmeni t the other h a m the washi n b y sendin g i ional Conf e p hate process u t ion of h y dra t O 2 separatio n t ion is sep a u um filters c an be c o a ted for the g d etailed later . g : After the s e d TiO 2 cak e v e the rem a c id solution u d , in principl e p is then pla c r content an d o lid is coole d n el y g round c ommercial d t b y -product , – 25 % H 2 SO 4 a llizers, wh e r ous sulpha t nstitutes the mmonl y kno ng stron g reuse in the e d in this p ( MON ) , for rated b y filtr c acid can be t e di g estion s a nd, the we a ng of the Ti O i t into a neu e rence on A Madrid, 1 u sed in the Hu e t ed titanium. n : The h y dr a a rated from ( called “M o o nsidered g eneration of . s eparation o f e is washed w a inin g impuri t u sed in this f e , a waste o f c ed in rotar y k d some trac e d , milled, co a ( “microniz e d istribution. , i.e. the mo 4 ) is pumped e re the iro n t e heptah y d first co-pro d wn as coop e acid is t initial di g e s p rocess fer r min g a se c ation. Then, rec y cled an d s tep. a k sulphuric a O 2 pulp, it is a tralization pl A dvances in 2-13 Nove m S03-3 e lva factor y for a ted the o ore one two f the w ith t ies. f inal f the k ilns e s of a ted, e d” ) , ther into n is rate d uct e ras t hen s tion r ous c ond the d be a cid a lso ant, wh e we a re d dih h yd foll o Ca Fe S at foll o m a sla g t o f E X sla g (R G tita of ca m m o da y va r th e a c we h yd an a te c he a Materials R m ber 2009 TiO2 productio n e re b y the a a k acid stre a d gy psum ( hy drated cal c d roxides, whi o win g reacti o ( OH ) 2 +H 2 S O S O 4 +Ca ( O H The m a the Huelva o win g fi g ure a terial are p r g) , with the g f CAP and 1 2 X PERIMENT A The sa g) , co-produ G ) used in t h nium dioxid e Huelva, in s m pai g ns we o nth, takin g y s in order r iabilit y in th e e raw materi a c onstant we i re dried at d ration wate r The m a l y zed b y m c hnique. Th e a v y metals, R ecycling a n . a ddition of li m a m, it is g ene r ( RG ) , whic h c ium sulphat e ch g ive it a r e o ns: O 4 → CaSO 4 H) 2 → Fe ( OH ) ag nitude of t h factor y is s: annuall y , r ocessed ( 8 5 g eneration o f 2 5,000 t of M A L mples of ra w cts ( CAP a n h is stud y ha v e production s outh-weste r re or g anize d theses men t to anal y ze e industrial p a ls were drie d ig ht, while t h 45 °C to r . m ineralo g ic a m eans of the e concentrati and othe r nd Eco – E m e, or lime s r ated a solid h is forme d e (CaSO 4 ·2 H e d color, acc ·2H 2 O ) 2 +CaSO 4 h e co-produc t reflected cl e around 142, 5 % illmenit e f 70,000 t of R M ON. w materials ( i n d MON ) an v e been coll e plant 12 km r n Spain. Fi v d durin g a t ioned sam p the possi b p rocess. A ft e d at 105 °C u h e co-produ avoid the l o a l composi t X-ra y diffr a ons of ma jo r trace ele m nergy 80 s tone, to the waste called d mainl y o f H 2 O) and iron ordin g to the t s g enerated e arl y in the 000 t of ra w e and 15 % R G, 140,000 llmenite and d the waste e cted from a from the cit y v e samplin g period of 1 p les ever y 6 b le temporal e r collection, u ntil reachin g cts and RG o ss of thei r t ions were a ction ( XRD ) o r elements, m ents were f w y r 1st Spanish National Conference on Advances in Materials Recycling and Eco – Energy Madrid, 12-13 November 2009 S03-3 81 determined by X-ray fluorescence (XRF) and ICP-MS, respectively. Additionally, the activity concentrations of natural radionuclides in these materials were determined by both alpha-particle and gamma spectrometry with semiconductor detectors. RESULTS AND DISCUSSION In Table 1, we can see that ilmenite is a NORM mineral due to its enrichment by natural radionuclides from the Th and U series, with a total concentration of some 500 Bq/kg for 238U and 232Th. The figures for slag are lower than those found in typical undisturbed soil (20-30 Bq/kg) [7]. Table 1. Average concentrations of dry Bq/kg activity of natural radionuclides in the raw material, co-products and RG. Relative Humidity R.H (%). N.D. Under Detection. HR 238 U 226 Ra 232 Th 228 Ra 40 K ILM 4 95± 10 110±10 420±15 440±30 30±5 SLAG 3 5.9±0.6 6.1±0.6 14 ± 1 9.0±0.4 N.D CAP 40.3 1.5±0.2 N.D. 13 ± 2 4 ± 1 N.D. MON 4.2 53 ± 2 9.1± 0.4 365±13 43±2 N.D. RG 46.3 20 ± 1 14 ± 1 127 ± 3 91± 3 12±2 The CAP activity concentrations are less than 10 Bq/kg, so its use in any application is not restricted by its radioactive properties. By contrast, MON has high levels of Th isotopes, particularly 232Th and 228Th, as well as an appreciable fraction of the initial U that enters the process with the ilmenite. The radioactive content for RG) is moderate, indicating that a minority fraction of the initial content (for the Th and U isotopes) in the treated raw material accumulates in this co-product. In relation to the majority metals, ilmenite has the following composition: Fe2O3 (44 %) and TiO2 (50 %), with low percentages of SiO2 (0.7 %), MnO (1.3 %) and MgO (0.33 %), [4]. By contrast, the slag is much richer in titanium than the ilmenite (75 % TiO2), as expected, but poorer in iron (11 % F2O3) [6]. On the other hand, CAP (FeSO4·7H2O) and MON (FeSO4·1H2O) yield high percentages of iron (~ 30 %) and sulphur (~ 25 %), as expected, which corroborates what XRD obtained. Due to its formation process, the CAP (achieved by crystallization) contains a lower proportion of metals than the MON (by precipitation). The levels of radionuclides and heavy metals in CAP and MON are not a problem in present commercial applications. Copperas is currently being used as a basic soil amendment, animal feed and a primary flocculant in the production of liquid and solid ferrous sulphate for waste water treatments. As for the monohydrate, it is valued as a fertilizer for soils that are poor in iron, and as an additive in the cement industry for the reduction of Cr (VI). Lastly, the majority composition of RG is: 27 % SO3 and 33 % of CaO, with CaSO4·2H2O being the dominant crystalline phase, but with a significant iron hydroxide content (12 %) which gives it its characteristic dark red colour [8]. Also surprising is this co-product’s high titanium content (~7 % TiO2), which has led the industry to seriously investigate ways of recovering it. Research is currently focused on replacing natural gypsum in cement with red gypsum (clinker + natural gypsum) as a setting retardant. The first trials have begun, with the mixing of 10 % RG with 90 % clinker (RG1) and comparing the result with Type I (95 % clinker) 52.5 N/SR commercial cement (CEM). Table 2 shows the preliminary results of tests for resistance and setting time. The behaviour of the RG sample studied is similar to that of commercial cement, and the figures fall within the RC-08 Spanish Regulations. Tabla 2. Figures relating to bending and compression (MPa). Initial setting time Ti, final Setting timeTf (min). Bending Compression Setting 2days 28days 2 days 28days Ti T f CEM 6.8±0.3 10.1±1.2 34.4±0.4 61.3±1.0 139 224 RG1 7.6±0.8 10.8±0.8 31.5±0.8 59.6±1.5 216 351 In order to carry out the radiological evaluation and to check what kind of material can be used in construction, the EU has established criteria in its “Radiation Protection 112” document [9] that defines the rate of external risk (I) as: 1 3000 40 1 200 228 1 300 226 − + − + − = Bqkg k C Bqkg Ra C Bqkg Ra C I where C226Ra, C228Ra, C40K are the concentrations of the activities of 226Ra, 228Ra and 40K, respectively, in the construction material on trial. When applying this radiological criterion, we find that red gypsum can be used as a component of construction materials in any proportion with no radiological consequences. 1st Spanish National Conference on Advances in Materials Recycling and Eco – Energy Madrid, 12-13 November 2009 S03-3 82 CONCLUSIONS The present study has been made to acquire detailed information on the composition of raw materials, co-products and waste from the process to obtain TiO2. Once these three have been typified from the physical, chemical and radiological viewpoint, we have confirmed that the concentrations of metals and radionuclides in the CAP and MON co-products are within the European regulations pertaining to applications. RG, is now being used as a substitute for natural gypsum in cement production. The preliminary results indicate that it can be used without the cement losing any of its mechanical properties. REFERENCES [1] L. Kacimi, A. Simon-Masseron, A. Ghomari, Z. Derriche (2006). Reduction of clinkerization temperature by using phosphogypsum, Journal of Hazardous Material B137 129–137. [2] Y. Liu, C. Lin, Y. Wu (2007), Characterization of red mud derived of from a combined Bayer process and bauxite calcination method, Journal of Hazardous Materials 146 255–261. [3] E. Deydier, R. Guilet, S. Sarda, P. Sharrock (2005) Physical and chemical characterization of crude meat and bone meal combustion residue: “waste or raw material?”. Journal of Hazardous Materials B121 141–148. [4] T. Chernet (1999). Applied mineralogical studies on Australian sand ilmenite concentrate with special reference to its behavior in the sulphate process. Minerals Engineering, Vol 12. No 5, 485-495. [5] Sahoo, P.K., Galgali, R.K., Singh, S.K., Bhattacharyee, S., Mishra, P.K., Mahanty, B.C., (1999). Preparation of titania-Rich Slag by plasma smelting of ilmenite. Scand. J. Metal. 28, 243– 248. [6] P.C. Pistorius, C. Coetzee (2003). Physicochemical aspects of titanium slag production and solidification, Metallurgical and Materials Transactions B 34B 581–588. [7] United Nations Scientific Committee on the effects of Atomic Radiation (UNSCEAR) (2000). Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, United Nations, New York. [8] I. Fauziah, S. Zauyah, T. Jamal (1996), Characterization and land application of red gypsum: a waste product from the titanium dioxide industry, The Science of the Total Environment 188 243–251. [9] EC, (1999) Office European Comission Report on Radiological Protection Principles concerning the natural radioactivity of building materials, Radiation Protection 112, for Official Publications of the European Communities, Luxembourg. ACKNOWLEDGEMENTS We are grateful to Huntsman-Tioxide S.L. and the Eduardo Torroja Institute of Construction Sciences (IETcc) for its collaboration.