The goal of this study is to find a practicable way to recycle cuttlebone waste in the production of lime. It was studied the behavior of calcium oxide obtained from the calcination of this waste at 900, 1000 and 1100 ºC and, after wet slaking, the produced lime was characterized. All the results were compared to calcium oxide or to hydrated lime obtained from commercial limestone. According to the slaking results, the waste and the limestone calcined at 1000 ºC achieved the R4 (around 13 min to reach 60 ºC) and R5 (60 ºC in 25 s) reactivity class, respectively. Changing the calcination temperature to 900 or 1100 ºC did not promote an increase in the reactivity of the calcined waste. Although less reactive than the calcined limestone, the calcined cuttlebone can be transformed without significant constraint into building lime, since this construction material fulfills the relevant physic-chemical standard specifications.
The calcium carbonate-rich shell, a biogenic excretion, secreted by some living organisms is a hard protection which makes part of the body of the animal. In general, the term seashell is correlated to the exoskeleton (external shell) of marine invertebrate animals, but in strict sense could be associated to both external or internal shells of marine molluscs. While most seashells are external, cephalopods of the
The cuttlebone consists of two different sectors: the upper part called the dorsal shield (or horny layer or hypostracum) and the lower part called the ventral chamber (or lamellar matrix or siphuncular) (
In the past, cuttlebone was ground up to make polishing powder used by goldsmiths, added to toothpaste, as anti-acid for medicinal purposes, as an absorbent or as an artistic carving medium. Traditionally, jewellers and silversmiths use it as moulds for casting small objects or in the process of pewter casting.
Nowadays, cuttlebone is commonly used as calcium-rich dietary supplement for pet animals (birds, reptiles, crabs, shrimps and snails). The design of biomimetic materials based on cuttlebone structure has been suggested (
The cuttlebone is mostly composed of aragonite, an orthorhombic calcium carbonate polymorph, involved by 3.0-4.5 wt% of organic compounds (
Due to its value for human diet, cuttlefish species are worldwide captured and produced (aquaculture) with a global landing value around 440 340 t for the year 2017 (
Since cuttlebone is essentially composed of calcium carbonate, it has high potential, similarly to other carbonate-rich wastes (geologic or biogenic origin), to be used as raw material in the production of calcitic building lime. Building lime is defined, according to NP EN 459-1 standard (
In this sense, it was studied the wet slaking behaviour of cuttlebone waste calcined at three distinct temperatures (900, 1000 and 1100 ºC). The aim is to use this residue in the production of building lime. Recycling cuttlebone will transform this waste into an eco-binder construction product, fulfilling the principles of a circular economy, aligned with the concept of cleaner production.
The cuttlebone waste, obtained from the European common cuttlefish (
The waste (~950 g), previously washed with tap water, and the commercial limestone (~900 g) were dried at 105±5 ºC (Memmert UF110), coarsely crushed in a porcelain mortar, milled in a tungsten grinder (Retsch RMO 100) for 3 min and sieved at 38 μm. The resultant powders were thoroughly characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF) spectrometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR) spectroscopy, and Raman spectroscopy, following the flowchart previously reported (
XRD was performed on a Philips X’Pert PRO MPD diffractometer operating with CuKα radiation at 50 kV and 30 mA. Diffractograms were recorded with a scan rate 0.02 °θ/s in the range 4°-65° 2θ. Crystalline phases were identified by comparison with the powder diffraction files from the International Centre for Diffraction Data. Chemical analysis of the major and minor elements by XRF was carried out using a PANalytical equipment PW 4400/40 Axios with CrKα radiation. A pressed disc (≈ 115 MPa) containing 6-10 g of powder and 4-5 drops of polyvinyl alcohol with about 4 cm diameter and 0.5 cm height was prepared for analysis. The loss on ignition (LOI) was determined gravimetrically, by calcinating the sample at 1000 °C for 3 h in ambient (oxidizing) atmosphere. TGA and DSC were performed simultaneously on a Netzsch Jupiter STA 449C apparatus, under oxidizing (air) atmosphere, between 20 and 1000 °C at a heating rate of 10 °C/min. FTIR spectra were recorded on a Bruker Alpha spectrometer in the 400–4000 cm-1 range using 4 cm−1 resolution and 128 scans. Raman spectra (100–4000 cm-1 range, 4 cm-1 resolution and 200 scans) were obtained in a Bruker RFS 100/S FT-Raman spectrometer, equipped with YAG:Nd laser (1064 nm and 350 mW excitation source).
The cuttlebone waste and the commercial limestone were calcined at 900 ºC, 1000 ºC and 1100 ºC in a Nabertherm N 100/H laboratory kiln under air atmosphere (3 ºC/min of heating rate; 2 h of soak time). The calcined products were additionally milled in a porcelain roller ball mill during 15 min, and sieved at 250 μm, for the wet slaking tests.
The specific surface area and the morphology of the calcined products were evaluated. The specific surface area was determined by N2 adsorption at 77 K in a Micromeritics ASAP 2000 instrument. Samples were previously treated in a vacuum at room temperature before analysis. The morphology was evaluated by field emission scanning electron microscopy (FESEM) in a Carl Zeiss Merlin microscope, in secondary electron mode. An acceleration voltage of 2 kV and working distance of 6.6 mm were used and the samples were previously sputter-coated with gold (
The quicklime powders were submitted to the wet slaking reactivity test according to NP EN 459-2 standard (
t60, time (min) for a suspension of CaO (150 g) and water (600 g) to reach 60 ºC;
reactivity class, classification of the CaO reactivity according to the time (min) to reach 60 ºC: R5 class if less than 10 min or R4 class if between 10 and 25 min;
T’maximum, maximum temperature (ºC) reached during the test;
Tmaximum, maximum temperature (ºC) corrected for the water equivalent of the apparatus: Tmaximum = (1.1 × T’maximum) - 2;
Tu for 80% of the reaction, temperature (ºC) for 80% of the reaction, calculated as: Tu = (0.8 × T’maximum) + (0.2 × T0), where T0 (°C) is the initial temperature of the water (~20 ºC);
tu for 80% of the reaction, time (min) for 80% of the reaction, obtained by the wet curve.
The hydrated limes obtained after the slaking test (for calcination at 1000 ºC) were evaluated regarding their expansion behaviour, according to NP EN 459-2 standard (drying at 150±5 ºC, for 4 h, under air atmosphere) (
Bulk XRD of the raw cuttlebone sample (
XRD patterns of the raw and lime materials from cuttlebone and limestone with the identification of phases.
The chemical analysis by XRF (
XRF data (in wt%) of the raw and lime materials from cuttlebone and limestone.
Sample | CaO | MgO | Na2O | K2O | SiO2 | Al2O3 | Fe2O3 | P2O5 | SO3 | Sr | Cl | LOI |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Raw limestone | 55.23 | 0.38 | 0.04 | 0.01 | 0.20 | 0.12 | 0.06 | 0.01 | 0.06 | 0.01 | nd |
43.87 |
Raw cuttlebone | 53.37 | 0.15 | 0.76 | 0.05 | 0.15 | 0.06 | 0.05 | 0.09 | 0.20 | 0.32 | 0.27 | 44.51 |
Lime | 81.69 | 1.25 | 0.09 | 0.04 | 0.22 | 0.11 | 0.17 | 0.01 | 0.16 | 0.02 | 0.02 | 16.23 |
Cuttlebone lime | 76.74 | 0.29 | 0.11 | nd |
0.05 | 0.01 | 0.01 | 0.08 | 0.31 | 0.39 | 0.01 | 21.89 |
MnO and TiO2 were also analysed in all the samples but not detected.
LOI: loss on ignition
nd: not detected
The weight loss in the thermogravimetric plot of cuttlebone (
Thermogravimetric data for the raw cuttlebone and limestone samples.
Sample | Weight loss (%) |
CaCO3 |
|||
---|---|---|---|---|---|
Moisture |
Organic matter |
CO2 | Total |
||
20-110 ºC | 110-650 ºC | 20-1000 ºC | (%) | ||
Raw limestone | 0.1 | 0.1 | 43.9 [650-915 ºC] | 44.2 | 99.8 |
Raw cuttlebone | 1.0 | 3.6 | 40.8 [650-860 ºC] | 46.1 | 92.8 |
Thermal analysis results for the raw cuttlebone and limestone samples: a) Thermogravimetry (TG) plot and derivative curve (DTG); b) Differential scanning calorimetry (DSC) and derivative curve (DDSC).
Cuttlebone FTIR spectrum (
FTIR spectra of the raw and lime materials from cuttlebone and limestone.
Finally, the Raman spectrum (
Raman spectra of the raw cuttlebone and limestone samples.
The cuttlebone waste and the limestone sample were calcined at three temperatures: 900, 1000 and 1100 ºC, with 2 h soak time.
FESEM microphotographs of the calcium oxide particles obtained after calcination of: limestone (20000 magnification) at 900 ºC (a), 1000 ºC (b) and 1100 ºC (c); cuttlebone (2000 magnification) at 900 ºC (d), 1000 ºC (e) and 1100 ºC (f).
The size of the calcined particles of cuttlebone was markedly larger than the size of the calcined particles of limestone, as evident by the comparison of the SEM images of the calcined cuttlebone samples with those of the calcined limestone samples, with an ampliation ten times larger (d, e and f
The BET specific surface area of the limestone calcium oxide samples decreased with increasing calcination temperature: 10.7 m2/g at 900 ºC, 5.2 m2/g at 1000 ºC and 2.3 m2/g at 1100 ºC. This agrees with the SEM microscopy results shown above, with smaller particles providing higher specific surface area. For the calcined cuttlebone, the magnitude of the BET values was lower: BET specific area was fifteen times lower at 900 ºC (0.7 m2/g), five times lower at 1000 ºC (1.0 m2/g) and two times lower at 1100 ºC (1.1 m2/g). This is in agreement with the great particle size difference between the two materials, shown by SEM. The larger and more aggregated particles of calcium oxide from cuttlebone promote a lower specific surface area. However, it is noteworthy that when calcination temperature was increased to 1100 ºC, the BET values of both calcined materials approached each other. Again, this could be an evidence of the sintering stage.
Wet slaking tests were performed for the calcined cuttlebone samples and the calcined limestone. For the calcined limestone the temperature of 1000 ºC was chosen, since this is the temperature usually used as reference in laboratory experiments. In the case of cuttlebone waste it was decided to change the calcination temperature, once for the tests with sample calcined at 1000 ºC the reactivity was not very high. Thus, temperature was increased and decreased of 100 ºC relatively to the reference temperature. For the calcined limestone a remarkably high reactivity was already obtained for the calcination at 1000 ºC (
Wet slaking curves of the calcined cuttlebone and calcined limestone samples.
The behavior of CaO from limestone was already described elsewhere (
Wet slaking parameters for the calcined cuttlebone and calcined limestone samples.
Sample | Calcination temperature (ºC) | t60 (min:s) |
Reactivity class | T’maximum (ºC) |
Tmaximum (ºC) |
Tu, 80% reaction (ºC) |
tu, 80% reaction (min:s) |
---|---|---|---|---|---|---|---|
Limestone CaO | 1000 | 00:25 | R5 | 76.6 | 82.3 | 65.3 | 00:28 |
Cuttlebone CaO | 900 | 14:41 | R4 | 75.9 | 81.5 | 64.7 | 15:46 |
1000 | 13:09 | R4 | 76.7 | 82.4 | 65.4 | 14:22 | |
1100 | 14:39 | R4 | 76.7 | 82.4 | 65.4 | 15:56 |
t60 – time to reach 60 ºC
T’maximum – maximum temperature reached
Tmaximum – maximum temperature reached, corrected using Equation [1]: Tmaximum = (1.1 × T’maximum) – 2 [1]
Tu, 80% reaction – temperature for 80% of the reaction, calculated by Equation [2]: Tu = (0.8 × T’maximum) + (0.2 × T0), where T0 (°C) is the initial temperature of the test (~20 ºC) [2]
tu, 80% reaction – time for 80% of the reaction, obtained by the wet curve
Apparently, increasing calcination temperature from 1000 to 1100 ºC for cuttlebone seems to slightly retard the hydration curve (
When calcining cuttlebone at 900 ºC some difficulties were found in obtaining reproducible wet slaking curves. The referred temperature could be insufficient to achieve calcium oxide particles with homogeneous physicochemical properties. The temperature of 900 ºC is also very close to the offset of CaCO3 degradation temperature (~860 ºC) determined by thermogravimetry (
The lower reactivity of cuttlebone
The slaking curve of the calcium oxide from cuttlebone exhibited a ‘‘S’’ pattern by opposition to a ‘‘line’’ pattern of the calcined limestone. The hydration rate of the calcined materials is influenced by the two induction periods underlying the slaking process. The slaking of the CaO from limestone is developed in one step, as previously reported (
In the slaking of the calcium oxide samples it was not noted any relevant variation in the thickening of the suspensions.
The lime suspensions were dried to obtain hydrated lime in powder form. For both materials, the characterization by XRD showed portlandite, as main phase, and vestigial contents of calcite. In the case of lime from limestone, traces of brucite were also detected, formed by the hydration of magnesium oxide present in the calcined material (
XRF data (
Both FTIR spectra (
Finally, limes color properties were analyzed. The coordinates for the lime from limestone were L*=97.39, a*=-0.02 and b*=1.21. For the lime from cuttlebone a slightly higher lightness (L coordinate) was obtained (98.22). The values for the coordinates a* (-0.16) and b* (0.09), indicated a negligible shift to the green and to the yellow, respectively. The color results for the lime from cuttlebone, overall, point out to a white tonality material.
The hydrated lime powder from the waste material is in accomplishment with the specifications reported in the building lime standard.
Final considerations should be paid to the incorporation of the cuttlebone waste in the process of building lime production at industrial scale. Although the quicklime from cuttlebone waste was less reactive than the quicklime from limestone, it is not expected that the mixture of cuttlebone waste and limestone would highly reduce the quality of the final produced lime, since the residue would always be incorporated in a small proportion relatively to limestone. This takes into account the lower amounts of available residue, in comparison to the quantities of limestone needed to feed a lime factory: a common Portuguese lime factory needs ~1643 t by day of limestone to reach an average daily production of ~920 t of quicklime (
This work introduces a cleaner production practice of transforming cuttlebone waste into a building material for a sustainable construction, when compared with traditional process of lime production from limestone source. The raw material was composed by aragonite (~93 wt%), with halite as contaminating phase. Some amount of organic matter (~4 wt%) was also present.
The evaluation of the wet slaking behavior of the cuttlebone waste after calcination at several temperatures (900, 1000 and 1100 ºC) showed that it is possible to use it as a calcium carbonate source to produce building lime. However, the reactivity class was lower (R4) than that of calcium oxide from limestone (R5). There was not a significant effect of the calcination temperature on the wet slaking reactivity of the calcium oxide from cuttlebone. In fact, increasing temperature from 1000 to 1100 ºC or decreasing temperature down to 900 ºC, even seemed to decrease slightly the reactivity, although not statistically significant. Overall, the calcination temperature of 1000 ºC may be considered near the optimal one for the calcination of the waste material. The wet slaking curve of the cuttlebone waste had a “S” design, and the average time to reach 60 ºC was 13:09 min:s for the waste sample calcined at 1000 ºC.
The hydrated lime powder produced from the cuttlebone waste had a white tonality superior that of the lime produced from commercial limestone.
Using this waste in an industrial process of lime production enables its valorization in the construction industry, contributes to a sustainable exploitation of natural limestone, and, additionally, it represents an example of a circular economy application. In this way, the cuttlebone waste could partially replace, although in a small extent, the limestone commonly used in the process, while not significantly interfering with the restrictions and conditions underlying the industrial process of building lime production.
The authors thank VAC Minerais, S.A. (Rio Maior, Portugal) for supplying the commercial limestone, the support of Quadro de Referência Estratégica Nacional (QREN) and R&D units: Techn&Art (UID/05488/2018) and Geobiotec (UID/GEO/04035/2019).
They also thank Prof. Dr. Francisco Franco Duro, from the University of Malaga (Spain), for the translations to Spanish language.