Lifeceram Designs a Highly Sustainable Ceramic Tile Body Preparation Process

Lifeceram

Newsletter nº4

Lifeceram designs a highly sustainable ceramic tile body preparation process

One of the Lifeceram project’sfundamental objectives is to design a highly sustainable preparation process for the ceramic tile body composition.

The process is based on the use of dry milling and granulation technologies because these enable energy efficiency and energy savings to be optimised, while alsoconsiderably reducing natural resource consumptions.

In addition, thebody preparation process must be sufficiently robust and solid to enable all typesof ceramic wastesto be recycledand, of course, to be highly sustainable with regard to the current wet milling andspray drying process.

The current ceramic tile manufacturingprocess, including the body composition preparation stage, can be consulted at the following link:

The Lifeceram project thus focusesthe new process on waste pre-treatment, on the selection of the most appropriate typeof milling for each waste, and on the way granulation is performed.

What is granulation and why havewechosen this technology?

Granulating involves agglomerating the material in the form of granulesmade up ofsolid particles that can be observed at sight. Generallyspeaking, the granulation process consists of the following stages:

• Wetting and nucleation, in which the first contact between the liquid binder and the dry powder takes place to form the first granulate cores. The size and distribution of these initial coresdepend on the starting characteristics of the powder and the binder, on the granulation process, and on the operatingparameters of this first stage.
• Core growth, in which the collision between two coresor between core and powder leads to core growth and granule formation.
• Fracture, in which the granules break owing to impact or wear in the granulator or during subsequent granule handling.

Granulation is,environmentally,a low water and air polluting technology that provides about 80% saving in thermal energyand about 75% reduction in water consumption,compared with the suspension spray-drying process.

Lifeceram starts waste pre-treatment: typesof milling, typesof mills, and granulation.

The pre-treatment to be conducted on each waste was defined as a function its nature, particle size, and behaviour during the main ceramic tile manufacturing process stages.

The most appropriate type of milling was then determined for the main wastes considered: i.e. for unfired tile scrapand fired tile scrap, as these were deemed to be the most representative wastes of all the wastes studied in terms ofarising volumes and hardnesses.

Drymilling technologies were taken into account using three typesof mills: pendulum mill, hammer mill, and disc mill, with a view to minimising re-processing wastesthat already had an appropriate particle size. The best milling process was thus respectively selected for the waste with high hardness, such as fired tile scrap, and for the waste with low hardness, such as unfired tile scrap and glazeand polishing sludge.

Finally,the granulation stage of the mixture of wastes was studied, analysing the efficiency of two typesof granulators, with high- and low-energysystems, and then determining the propertiesof the resulting granules.

Which wastes were studied?

The wastesstudied in this action were the typical ceramic wastesthat are generated in ceramic tile manufactureand in related sectors (spray-drying plants and tile edge-grindingand polishingplants), together with wastes from thermal power stations and glass recycling plantsnear the Castellónceramic cluster. These wasteswere to be used in formulating the body composition.

Thefollowing wastes were involved:

a) Ceramic wastes

Unfired tile scrap.Thiswaste consists of unfired ceramic tiles that were broken in ceramic tile manufacturing plants, which may be glazed or unglazed, depending on where the scrap is generated. Figure 1showswhat this scrap looks like.

Figure 1. Unfired tile scrap generated in the lines

Extracted dust. Plants have dust extraction systems in the entire unfired tile processing zone (Figure 2) inwhich bag filters are used(Figure 3). The extracted dust is discharged directly into the hopper of the unfired tile scrap crusher.Given the low percentage of extracted dust with relation to the volume of unfired tile scrap (less than 5%) and their physical and chemical similarity, it was deemed convenient to treat the dust together with the unfired tile scrap.

Figure 2. Dust extraction system in the press zone /
Figure 3. Fabric filter baghouse fordust removal

Glazesludge. Glazesludge is collected by means of gutters under the glazing and decoration lines (Figure 4). The sludge isthen led through pipes to a glaze sludge decantation tank (Figure 5),yielding an aqueous suspension with a very low solids fraction (Figure 6) in addition to an aqueous sludge with a higher solids fraction.

Figure 4.Gutters in the glazing and decoration lines /
Figure 5.Glazing sludge waste tanks

Figure 6. Tank holding the aqueous suspension with a low solids content

Fired tile scrap.Pieces of fired tile are involved that are collectedin small skips like those for the unfired tile scrap. At present,fired tile scrap is not separated bytype of product. Itis transferred to a large skip (Figure 7)that is then sent to awastehandler(at present fired tile scrap is not recycled).

Figure 7.Fired tile scrap for waste handling

Polishing sludge. At present, tile polishing and edge-grinding sludge is filterpressed (this is done using a special filterfor separating large volumes of solids and liquids by pressure filtration. The filterpress capabilityallows the solids to be dehydrateduntil about 65% by weight of compacted sludge is obtained in order to recycle the water). The resulting cakes are either landfilled or used as aggregate in preformed concrete products (blocks, joist-to-joist filler blocks, etc.). The size of the cake solids isusually below5 mm.

Kilnfilter dust. This is a particulate waste collected in the bag filters that clean hot kiln gases. These filters work using calcium compounds as reactiveelements.

Glazesand frits.Surplus inks and glazes are involved, which are storedafter given lots have been manufactured (Figures 8 and 9) and cannot be used because they lie outside specifications. The quantity of these wastes varies greatly and is small in relation to the amount of tile scrap. The composition of these wastes is very similar to that ofthe glazesludge, so that it was decided to also handle these together.

Figure 8.Surplus screen printing inks /
Figure 9. Surplus glazes

b) Non-ceramic wastes

Fly ashes from thermal power stations. These are particulatematerials consisting of glass and coal combustion waste. Figure 10 shows what this waste looks like.

Figure 10. Appearance of fly ashes

Recycled glass.Of the different types of recycled glass, the most appropriate for incorporation into the body is hollow container glass. This glass can be suppliedeither untreated(Figure 11)or ground to different particle sizes (Figure 12).

Figure 11. Recycled glass /
Figure 12.Ground recycled glass

Pre-treatment to be performed for each waste.

Table 1details the pre-treatmentthat needs to be performed on each wasteprior to milling, as a function of the nature of each waste:

Table 1. Required waste pre-treatment.

Type of waste / Appearance / Moisture content (%) / Particle size of the material (µm) / Hardness of the solid / Pre-treatment
Unfired tile scrap / Broken tiles / 0–3 / < 100 / Low / Crushing with notched rollers
Extracted dust / Powder / 0–2 / < 100 / Low / Unnecessary
Non-hazardous aqueous sludge / Sludge / Solids content: 20–30 % / < 100 / Medium / Magnetic separation + Sieving at 150 µm + Filter pressing
Aqueous suspensions / Aqueous / Density 1.06 g/cm3 / < 100 / Medium / Magnetic separation + Sieving at 150 µm + Filter pressing
Glazes / Suspension / Density 1.60 g/cm3 / < 100 / Medium / Magnetic separation + Sieving at 150 µm + Filter pressing
Fired tile scrap / Broken tiles / < 1 / Consolidated material / Medium–High / Jaw crusher
Polishing and edge-grinding sludge / Sludge / 20–25 / < 500 / Medium–High / Magnetic separation + Filter pressing (previous sieved)
Kiln filter dust / Powder / <1 / < 100 / Low / Unnecessary
Fly ashes / Powder / <1 / < 100 / Medium / Unnecessary
Recycled glass / Granular / <1 / Consolidated material / Medium–High / Jaw crusher

Waste milling

In this task, different types of dry milling were tested to determine the most appropriate type of milling for each waste. As the composition was based on unfired and fired tile scrap, the tests were conductedusing these two typesof waste asrepresentative of soft and hard waste. The following typesof milling werestudiedfor unfired and firedtile scrap, respectively.

Unfired tile scrap:

• Bladeimpact mill (hammer mill)
• Pendulum mill

Fired tile scrap:

• Blade impact mill (hammer mill)
• Disc mill

Granulation

In this task, different types of granulators were tested to determine the most suitable granulation facility. For the sake of simplicity,the tests were conducted using a composition with 50:50unfired and fired tile scrap.

The following typesof granulation werestudied:

• High-speed granulation (Granulator 1)
• Moderate-speed granulation (Granulator 2)

The samples of granulates obtained in each granulator, under the conditions used,were characterised by the following tests:

• Granulate moisture content
• Particle size distribution by the dry method
• Determination of the Hausner ratio
• Dry bulk density
• Dry mechanical strength
• Determination of the variation of bulk densityand water absorption with temperature

Conclusions

The following conclusions may be drawn:

• For the milling of soft materials it is advisable to use a hammer mill for moderate particle sizes (particle size cut-off at 200–300 µm) and to use a pendulum mill when the particle size cut-off needs to be about 100 µm.
• If hard materials are to be ground to a large particle size,it is advisable to use a hammer mill because of its greater cost effectiveness (size/costratio).
• The high-speedgranulator yieldsnarrower granule sizes, centred in the fraction 300-500 µm, which is the fraction it is soughtto maximise. The increased granulation speed in the low-energy granulator reduces the small fractions, but significantly increases the coarsest fractions, yielding a wider distribution.

AboutLIFECERAM

LIFECERAM is a LIFE+project, coordinated by the Instituto de Tecnología Cerámica (ITC), with the participation of the Spanish Ceramic Tile Manufacturers’ Association (ASCER) and the companies CHUMILLAS TARONGI, S.A., KEROS, S.A., and VERNÍS, S.A., which manufacture ceramic machinery; ceramic tiles; and frits, glazes, and ceramic colours, respectively. The projectseeks to achieve zero wastethroughout the ceramic tile manufacturing process. For further information on LIFECERAM+, please check out:

ITC Instituto de Tecnología Cerámica

Campus Universitario Riu Sec | Av. Vicent Sos Baynat s/n | 12006 Castellón (Spain)
T. +34 964 34 24 24 | F. +34 964 34 24 25 |

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