Cr-Doped Perovskite and Rutile Pigments Derived from Industrial By-Products

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Chemical Engineering Journal 171 (2011) 1178–1184

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Chemical Engineering Journal

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Cr-doped perovskite and rutile pigments derived from industrial by-products

a,∗ b a b a

W. Hajjaji ,C.Zanelli , M.P. Seabra ,M.Dondi , J.A. Labrincha

Ceramics and Glass Engineering Department, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

Istituto di Scienza e Tecnologia dei Materiali Ceramici, CNR-ISTEC, 48018 Faenza, Italy

a r t i c l e i n f o a b s t r a c t

Article history: In order to enhance the use of environment-friendly materials and to stimulate waste recycling, this work

Received 20 January 2011

has developed brown-maroon inorganic pigments belonging to rutile (TiO2) and perovskite (CaTiO3)

Received in revised form 13 April 2011

structures. They were obtained by solid state reaction of industrial residues mixtures: tionite (i.e. insol-

Accepted 9 May 2011

uble residue of titania slag processing), Cr/Ni plating sludge and marble cutting/sawing sludge, for sake

of comparison, analogous formulations were prepared by using reagent-grade precursors. Chromium-

Keywords: ◦

doped (0.04 mole of Cr2O3) perovskite and rutile pigments were obtained at 1200 C and their phase

Sludges

composition, microstructure, optical properties and technological behaviour were characterized by XRD,

Pigments

SEM, DRS and application in glazes, respectively. The presence of impurities (e.g. Fe, Ni, Al, Si) in the wastes

Chromium doping

Perovskite induced the crystallization of secondary phases, like wollastonite (CaSiO3) and titanite (CaTiSiO5), whose

Rutile occurrence slightly shaded off the ﬁnal colouration of the waste-based pigments; a further addition of

chromium is required to improve their colouring power in transparent glazes. The diffuse reﬂectance

spectroscopy shows that the colour development, in both structures, is due to the partial substitution of

titanium by chromium in octahedral coordination.

1. Introduction can be utilized. Among Ti-bearing phases, rutile, TiO2, and per-

ovskite, CaTiO3, are promising structures which exhibit a brownish

Incorporated in glazes for wall and ﬂoor tiles or in unglazed colouration by doping with chromium, that can be tuned by further

porcelain stoneware, the ceramic pigments market is growing with addition of a counterion (W, Mo, Sb, Nb) to maintain the electrical

the huge production of ceramic products. As brown pigments, charge balance [19].

the most used are based on hematite (DCMA 3-06-7) manganese The perovskite structure, with the general formula ABO3, is

chrome antimony rutile (DCMA 11-46-7) and spinels (DCMA 13- built by a network of corner-linked BO6 octahedra and encloses

33-7, DCMA 13-37-7, DCMA 13-38-9, DCMA N. 13-48-7, DCMA large cavities that accommodate the A-cations [20,21]. For tita-

N. 13-51-7) [1,2]. The last two incorporate some toxic elements nium dioxide, different polymorphs are found in nature: brookite

(Co, Ni, Cr, Nb, . . .) that could be minimized or simply avoided by (orthorhombic symmetry), rutile and anatase (tetragonal symme-

investigation of new formulations, involving also technological and try) [22,23]. The rutile structure is based on six oxygen atoms

economic concerns. surrounding each Ti ion, then forming tetragonally distorted TiO6

The use of industrial wastes as raw materials for the formula- octahedra [23,24]. In this work, both perovskite and rutile struc-

tion of brownish ceramic pigments based on titania is assessed with tures are explored as inorganic pigments, using industrial wastes

the aim to improve the environmental sustainability of pigment as raw materials (or reagent-grade precursors as control), by inves-

production by recycling hazardous residues. Such investigation is tigating their structural and chromatic development as well as their

within a research programme on waste-based ceramic colourants colouring behaviour in ceramic glazes.

[3] that already concerned the following structures: spinel [4,5],

malayaite-titanite [6,7], and hibonite [8,9]. It follows a general

2. Experimental procedure

interest in the literature on the valorization of heavy-metal bearing

residues into high added value products [10–14].

Calcite (Calcitec), chromium (III) oxide (Riedel-de Haën), and

In the ceramic industry, brown pigments are mainly spinels

titanium dioxide (Kronos) were the reagent-grade precursors used

[15], but also rutile [16], perovskite [17], and pseudobrookite [18]

to prepare Cr-doped perovskite (PP) and rutile (PR) pigments. The

Cr2O3/TiO2 molar ratio was ﬁxed equal to 0.04 (Table 1). The

pigments synthesis followed a conventional ceramic route. The

∗

mixture of precursors was homogenized by ball milling (60 min),

Corresponding author. Tel.: +351 234370250; fax: +351 234370204.

◦

E-mail address: [email protected] (W. Hajjaji). dried at 100 C (24 h) then calcined in an electric kiln (Termolab) at

W. Hajjaji et al. / Chemical Engineering Journal 171 (2011) 1178–1184 1179

Table 1

Chemical composition of precursors and batch formulations of pigments.

Reagents Calcite Cr(III) nitrate Rutile M G T

Providers Calcitec Sigma–Aldrich Knoros Marble sludge Galvanizing sludge Tionite sludge

Chemical composition (wt.%)

SiO2 0.18 – – 1.12 0.20 28.19

TiO2 0.02 – 99.93 0.04 0.02 45.59

Al2O3 0.18 – – 0.25 0.14 3.44

Cr2O3 – 99.00 – – 20.60 0.05

Fe2O3 0.12 – 0.03 0.42 0.36 2.05

MgO 0.36 – 0.54 0.38 2,18

CaO 99.11 – – 97.44 14.92 3.32

MnO – – – – – 0.39

NiO – – – – 29.71 –

CuO – – – – 17.97 0.01

Na2O 0.02 – – – 1.29 –

K2O 0.02 – – 0.19 0.04 0.40

SO3 – – 0.02 – 2.71 14.38

P2O5 – – 0.02 – 11.66 –

Batch composition (wt.%)

PP 55.6 1.7 42.7 – – –

SP – – – 40.7 4.3 55.0

SP2 – – – 40.1 6.4 53.5

PR – 3.8 96.2 – – –

SR – – – 7.2 92.8

SR2 – – – – 7.3 92.7

T1200 – – – – – 100

◦ ◦

the maximum temperature of 1200 C (5 C/min heating rate and interval 2 nm), using BaSO4 white as standard. These methods were

3 h dwell time). The ﬁred powders were manually ground and their also applied to a lead-free transparent bright glaze (SiO2, Al2O3,

particle size distribution was determined by a Laser Coulter LS230 B2O3, CaO as main constituents >8%, 2–8% Na2O, and <2% K2O)

granulometer. Analogous formulations (SP and SR) were replicated coloured with the perovskite or rutile pigment, which was added

by using industrial wastes: (i) marble sawing sludge, (ii) Cr/Ni gal- to the glaze (1/20 weight ratio), homogenized and pelletized, then

◦ ◦

vanizing sludge and (iii) tionite, whose compositions are reported ﬁred at 1050 C (5 C/min heating and cooling rate and 30 min dwell

in Table 1. In favour of comparison, the last sludge (tionite), under time).

the code T1200, was also calcined separately following the same

cycle.

3. Results and discussion

The pigments were characterized by quantitative phase anal-

ysis (XRPD, D8 ADVANCE, fast detector LynkEye Bruker AXS,

3.1. Pigment synthesis

Germany) under the following conditions: CuK␣ radiation in the

◦ ◦

10–80 2 range, scan rate 0.02 2, 185 s equivalent per step.

Differences in the thermal behaviour between PP and SP are

◦

The quantitative phase analysis was performed using GSAS-EXPGUI

detected at low-grade temperatures (<400 C). TG curves illustrate

software following RIR (Reference Intensity Ratio) and Rietveld

a mass loss reaching 15% in waste based mixture related to dehy-

reﬁnement techniques [25–27]. Each X-ray powder diffraction

dration reactions. PP and SP show a large endothermic peak (Fig. 1),

◦

pattern consists of approximately 5500 data points and 400

at about 850 C, due to decarbonation of calcite in both the pure

reﬂections. Up to 40 independent variables were reﬁned: phase

reagent and the marble sawing sludge (25% weight loss in the TG

fractions, zero point, 15–20 coefﬁcients of the shifted Chebyschev

curves). Minor effects on the DTA curve are observed at temper-

◦

function to ﬁt the background, unit cell parameters, proﬁle coef-

atures higher than 1000 C, but no mass changes on the TG curve

ﬁcients (one Gaussian, Gw, and one Lorentzian term, Lx). The

were registered; they probably stem from the reaction of rutile with

agreement patterns, as deﬁned in GSAS, were found in the fol-

calcium oxide to form perovskite [28]. These effects are less visible

lowing ranges: 9.0% < R < 13.0%, 13.0% < R < 16.5%, 6.0 < < 11.0,

p wp in the SP formulation (Fig. 1). In the waste-based compositions, the

and 11.0% < R(F2) < 15.0%. The experimental uncertainty of phase

SO2 evolution was expected due to incomplete decomposition of

◦

amount quantiﬁcation is 5%.

sulphates above 1200 C, as suggested by the weight loss registered

A scanning electron microscope (SEM, Hitachi, SU 70) equipped

on TG. This reaction may be partially hidden by the exothermic

with XRF-EDS microprobe (Bruker AXS, software: Quantax) was

peak related to the perovskite formation (on DTA). The volatiliza-

used to assess the microstructure and composition of pigment

tion of some sulphur oxide is not novel in the industrial practice,

particles. Inductively coupled plasma emission spectrophotome-

because the pigment synthesis is usually promoted by mineralizers,

try (ICP) was carried out by a Horiba Jobin Yvon (Activa M model)

i.e. mostly alkaline and alkaline-earth halogenides and sulphates

equipment to verify the chemical composition of pure obtained

[2,15], so that ﬂue gas scrubbers are already in operation on kilns.

pigments. The analytical solutions were obtained by microwave

In the PR mixture, the total weight loss is less than 2% and it is

assisted acid digestion. Their thermal behaviour was investigated

basically due to the release of physically adsorbed water. On the

◦ −1 ◦

by DTA and TG simultaneous analyses (in air, 10 C min heating

DTA curve, the peaks occurring above 900 C are probably related

rate) performed on a Setaram apparatus.

to the anatase-to-rutile transition, which allows the chromium

The L*a*b* [L*: 0 = black/100 = white, green (−a*) to red (+a*)

insertion into the lattice [29]. In contrast, the SR mixture under-

−

and blue ( b*) to yellow (+b*)] chromatic parameters, measured

went to signiﬁcant transformations upon heating, mostly caused

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by a Konica-Minolta Chroma Meter CR-400 (D illuminant and

65 by decomposition of hydroxides (around 300 C) and sulphates

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10 standard observer), were used to quantify the colour charac-

(around 1100 C) contained in the tionite sludge. The respective

◦

teristics of the pigments. The colouring mechanisms were studied

weight loss measured up to 500 C reached about 15%; and is close

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by UV–Vis–NIR absorption spectroscopy (Shimadzu UV-3100, step

to 7% between 1000 and 1200 C. Download English Version: https://daneshyari.com/en/article/150913

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