International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste
21-23 June 2017, Delft University of Technology, Delft, The Netherlands
25
Separation in air jigs of mixed construction and demolition waste
W. M. Ambrós
1, C. H. Sampaio
1, B. G. Cazacliu
2, G. L. Miltzarek
1, L. R. Miranda
3 1Federal University of Rio Grande do Sul, Center of Technology, Mineral Processing
Laboratory, Porto Alegre, Brazil
2
LUNAM, University of Nantes, IFSTTAR, Aggregates and Materials Processing
Laboratory, Nantes, France
3
Department of Civil Construction, Federal University of Paraná, Brazil
Abstract
Air jigging technology has been highlighted as a promising method for the sorting of recycled
aggregates from CDW. In this study, the broadening of its application for CDW recycling by
the combined removal of unwanted stony materials and low-density organic compounds is
discussed. Tests were performed with binary mixtures containing concrete and brick particles
in which gradual portions of gypsum, wood and paper were added. Experimental results have
evidenced that under different operational conditions and using different contamination level
it was possible to separate both the stony fraction and low-density materials in one single
stage. The content of contaminants used in the system seemed do not have significant effect
on the separation performance. Also, the separation extent was slightly sensitive to the
jigging cycle used. In relation to the sorting of organic contaminants only, the performance
obtained with the air jig can be considered comparable to that of sensor-based sorting and air
classifiers systems. Further investigation should focus on appropriate device and process
adjustments seeking the practical application of the technique in recycling plants.
Keywords:
Air jigging, Multi-component separation, Mixed waste.
Introduction
Recent studies [1, 2] has pointed out the air jigging as a promising technique for quality
improvement of coarse recycled concrete aggregates (RCA). Among the benefits of using air
jigging instead of other more traditional processes are the absence of processing water,
resulting in environmental and economical advantages, and the satisfactory results observed
in pilot-scale experiments [2]. For instance, Sampaio et al. [2] obtained products containing
more than 90% in mass of pure concrete from mixtures previously contaminated with brick
and gypsum. However, even though it is a cheap option compared to wet based processes, air
jigs can represent a considerable fraction of purchase and operational costs in a typical
recycling plant [1]. Given the importance of become RCA more competitive, the search for
solutions to upgrade its quality while keeping recycling costs at a minimum is mandatory. In
parallel, since air jigs have shown a good performance in the removal of stony contaminants
from concrete, the separation of lighter materials commonly found in mixed construction and
demolition wastes (wastepaper, wood, plastics, etc) is potentially a simple task. The success
of this strategy could result in economical and technical benefits since it would concentrate
the removal of several contaminants in only one process step, thus making the recycling
process simpler. In order to evaluate such possibility, the objective of the present work is to
examine the capability of air jigs to simultaneously carry out the separation of stony and
International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste
21-23 June 2017, Delft University of Technology, Delft, The Netherlands
26
stony impurities from concrete in only one single stage. The sorting results are encouraging
since they seem to demonstrate the potential of air jigging devices for use in multi-component
separation.
Experimental setup
The tests were carried out in a pilot scale air jig model AllAir® S-500 from AllMineral with
capacity of approximately 50 kg per batch. The jigging system is composed by an air feeding
unit, a separating chamber, dust collect unit and control panel. During operation, the particle
bed placed inside the separating chamber (Fig. 1a) is submitted to pulsations generated by an
airflow which enters through a perforated plate under the bed, being controlled by a flutter
valve. After several pulses, the differences in grain motion of particles derived from their
different densities result in a stratified bed with the heavier particles located in the lower
layers and the lighter ones in the upper layers.
The materials used in the tests consisted of binary mixtures of concrete (type 30 Mpa at 28
days) and brick in the size range of 12-20 mm in which pre-determined quantities of gypsum,
wood and paper were added. The bulk volumes of concrete and brick were choose as that
necessary to completely fill two layers of the separating chamber (500 x 500 x 25 mm),
corresponding to approximately 13,500 g of brick and 18,300 g of concrete (Fig. 1b). Wood
and wastepaper were comminuted manually in order to avoid the presence of larger pieces
inside the system.
(a) (b)
Figure 1 - Mixture placed inside the separating chamber (a); Sampling configuration used during the tests (b).
Five mixtures containing increasing amounts of contaminants were prepared: 0%, 1%, 2.5%,
4.6% and 9% in mass percent of the total mixture. Among the contaminants, the mass
proportions were kept in 40% of gypsum, 40% of wood and 20% of wastepaper. Operational
conditions were kept constants and equal to 160 RPM (pulse frequency), 80% (airflow,
measured in percentage of fan power) and 120 s (jigging time). After each test, the products
contained in the layers were collected separately and carefully separated by hand. The
separation extent was evaluated based on the composition of each stratum.
International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste
21-23 June 2017, Delft University of Technology, Delft, The Netherlands
27
Results
Experimental results indicated that the air jig was able to effectively remove both the stony
and non-stony undesired contaminants. Also, the initial content of contaminants seems to
have a negligible effect on the separation performance. Except in case of absence of light
contaminants, the general separation profile consisted of a top layer covered by paper, wood
and gypsum, a middle layer plenty of brick and a bottom layer mainly composed of concrete
particles (Fig. 2). For the specific case illustrated in Fig. 2 (9% in mass of contaminants), the
top of the separating chamber was open in order to allow the pieces of paper to be carried out
by the airflow. As can be seen, virtually all the wastepaper was dragged out from the system.
(a) (b) (c)
Figure 2 - Top view of the products after jigging for 9% of impurities. (a) Top layer; (b) Middle layer; (c) Bottom layer.
The separation results for concrete are displayed in Fig. 3. The sorting performance was
evaluated in terms of concrete content and recovery (mass of concrete in the product related
to the total mass of concrete in the system). The effect of the variation of the cut point was
also evaluated. In this sense, two cases were taken into account: by considering as product
only the material contained in the layer 1 or by considering as product the material contained
in layers 1 and 2. For the five cases studied, the average purity and recovery of concrete in
layer 1 were of 90% (± 3%) and 49% (± 2%) in mass, respectively. If layer 2 is also sampled
as a product, then significant increases in concrete recovery is obtained at the expense of
increase in contamination degree. In this case, the average concrete content decreases to 80%
(± 3%) and the recovery degree increases to 84% (± 4%). For all mixtures, the products
obtained (one or two layers) contained less than 1% in mass of the most undesired
components (gypsum, wood and paper) and approximately 90% in mass of concrete, which
meets the requirements set out by several countries to classify the jig products as coarse RCA
[3].
Figure 3. Concrete content and recovery in function of the contamination level. 40% 50% 60% 70% 80% 90% 100% 40% 50% 60% 70% 80% 90% 100% 0% 1% 2% 3% 4% 5% 6% 7% 8% 9%
R
ec
ove
ry
(
%
m
as
s)
C
ont
ent
(
%
m
as
s)
Contamination level (% mass)
Concrete content (only layer 1) Concrete content (Layers 1 & 2) Concrete recovery (only layer 1)
International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste
21-23 June 2017, Delft University of Technology, Delft, The Netherlands
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