ity separation, followed by nanometallic Ca/CaO pretreatment and
froth flotation separation.
A simplified flowchart for the selective separation of PVC is
given in Fig. 7. Initially, about 20.5 wt% of the light plastics PP
and PE can be separated from the E-waste plastics as a floated
fraction, by means of simple wet gravity separation. The remaining
79.5 wt% of heavy plastics are then subjected to nanometallic
Ca/CaO pretreatment followed by froth flotation, yielding a settled
fraction containing 100% of the PVC (7.02 wt% of the whole)
and a floating fraction containing the other heavy plastics. Total
recovery of non-PVC plastics reached nearly 100%, which is significantly
improved from the 20.5 wt% recovery of light plastics
when only wet gravity separation is applied. Most importantly, the
nanometallic Ca/CaO pretreatment and subsequent froth flotation
evidently separated even E-waste plastic particles of nonuniform
shape and size, yielding two fractions of PVC and PVC-free plastic.
Contrastingly, when other plastic surface modification methods
are used, entailing surfactant or other chemical treatment, optimized
size and shape are required to permit effective separation by
froth flotation [28–31,38,64]. Therefore, the simple and convenient
hybrid nanometallic Ca/CaO treatment and froth flotation method
described herein can be applied effectively to separate PVC from
other mixed E-waste plastics.
4. Conclusions
Selective surface hydrophilization of PVC by a nanometallic
Ca/CaO composite was successfully demonstrated in this study
as a means to allow separation of PVC from other E-waste plastics.
Nanometallic Ca/CaO treatment enhanced the wettability of
the PVC surface; the treatment made all plastics tested more
hydrophilic, but was quite selective for PVC, decreasing its water
contact angle by 18◦. SEM images of the plastics showed that
the treatment considerably changed the surface morphology and
roughness of PVC compared to other plastics. The SEM-EDS results
reveal that a markedly decrease of [Cl] concentration simultaneously
with dramatic increase of [O] on the surface of the PCV
samples. XPS analysis confirmed an increase of the hydrophilic
functional groups C O, C O, and (C O) O on the PVC plastic surface
after nanometallic Ca/CaO treatment. The treatment allowed
PVC to be separated from other E-waste plastics by means of froth
flotation;the plastics were separated into a PVC fraction and a PVCfree
fraction, even though the plastic particles were of nonuniform
size and shape. Under the condition of 100 rpm mixing, 100% of
the PVC settled, and the settled fraction was 96.4% PVC; thus, the
floating fraction was 100% PVC-free. The total recovery of nonPVC
plastics was nearly 100%, which is greatly improved from
the 20.5 wt% of light plastics that are recovered by conventional
wet gravity separation. Therefore, the hybrid nanometallic Ca/CaO
treatment and froth flotation separation developed herein is a simple
and effective method to separate hazardous chlorinated plastics
from E-waste. This convenient method will facilitate the industrial
application of plastics flotation, and the present work provides
technical insights into the process of hazardous chlorinated plastics
recycling.
Acknowledgment
This work was supported by the 2016 Research Fund of University
of Ulsan.