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TECHNOLOGY

flow rate of 1.0 mL/s released from reducing gases could be
calculated on average at the optimal roasting time of 450 s.
However, in light of the XRD pattern (Fig. 5a) and the mag-
netization curves (Fig. 4b), little contribution of the reducing
gases could be made in the remaining 350 s. Another notable
peak emerged in the range of 0–82 s because of the minimal
gas release. The preheating of the strawtype biomass and the
activation of cellulose, its main component, were the reasons
for this phenomenon and were also the inherent properties of
straw in the fast pyrolysis process [50,51].

Suspension magnetization roasting
and magnetic separation

Effect of roasting time

The effect of roasting time on SMR was studied with the time
varying between 2.5 and 15.0 min, the roasting temperature
at 700 C and a biomass doge of 25%. The SMR results in terms
0
of iron grade and the recovery of concentrate are displayed in
Fig. 3a. The iron grade and recovery increased with the exten-
sion of roasting time, showing the transformation of the mag-
netite phase. When the roasting time was 7.5 min, the grade
and recovery of iron concentrate were 69.86% and 94.41%,
respectively. However, when the roasting time increased
from 7.5 to 15.0 min, the iron grade percentage decreased to
69.23% with a slight increase in the recovery of concentrate.
The decrease in iron grade indicated that overreduction oc-
curred and magnetite was reduced to wustite during the SMR
process. Hence the optimal roasting time was determined to
be 7.5 min.

Effect of biomass dose

The effect of biomass dose on SMR was investigated within a
range of 10.0 to 35.0 wt%, a roasting temperature of 700 C,
0
and a roasting time of 7.5 min. The effects of biomass dose on
iron grade and recovery in magnetic concentrate are displayed
in Fig. 3b. When the dose of biomass increased from 10 to 30
wt%, the recovery of concentrate experienced a sharp rise.
However, the recovery dropped slightly when the dose of bio-
mass continued to increase. With increasing doses of biomass,
the iron grade increased slightly and peaked at 20 wt%. A rea-
sonable explanation for these observations is that excessive
biomass could easily over reduce the magnetite. The optimal
grade of 69.85% and recovery of 94.41% were determined at
a biomass dose of 20 wt%.
Fig. 4. Effects on saturation magnetization of roasted sample.
Effect of roasting temperature

were 168.96 and 172.63 mL, respectively. However, although The effect of the suspension magnetization roasting tempera-
both H2 and CO reached their peak volumes, the volume of H2 ture was investigated in the range of 450 to 900 C. The other
0
has a minor increase than that of CO and it can be estimated conditions were as follows: a biomass dose of 20 wt% and a
that the reducing gas flow ratio of H to CO was nearly 1:1. A roasting time of 7.5 min. The effects of biomass dose on iron
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