Samples of ductile iron alloyed with 0.88 % Ni with a nodule count of 606,
523, and 290 nod/mm2 were obtained from sand cast plates of different
thickness in the range from 8.46 to 25.4 mm. The effect of the nodule count
was evaluated during the austempering process held at 285?C and
austempering times of 15, 30, 45, 60, 70, and 90 min. The volume fraction of
high carbon austenite was increased when the nodule count was increased,
however, the carbon content of the high carbon austenite kept almost
constant. The process window was narrow, requiring a lower austempering time
when the nodule count was increased. The combination of a higher nodule
count and low austempering temperature allows obtaining a fine ausferritic
microstructure which leads higher Brinell hardness and tensile strength. The
process window was determined by XRD measurements and it is in good
agreement with the microstructural and hardness evolution as the
austempering time was increased.
Terminals obtained from spent lead-acid batteries in Mexico contain around 2
wt% Sb. The terminals were melted in an electric furnace and then oxygen was
injected to 750?C and a gas flow rate of 2 L/min to produce high purity
Sb2O3. The antimony trioxide obtained was treated with a mixture of
Na2CO3-SiC to 1000?C to obtain metallic antimony. The antimony trioxide is
reduced by the C present in reagents while silicon and sodium form a slag
phase. The amounts of Sb2O3 and SiC were held constant while the Na2CO3 was
evaluated in the range from 30 to 42 wt%. The antimony and slag produced
were characterized by X-ray diffraction and SEM-EDS techniques. The addition
of 34 wt% Na2CO3 leading the recovery of antimony up to 90.16 wt% (99.57 wt%
purity) and the lowest antimony losses in the slag (2 wt%). In addition, the
compounds Na2SiO3 and Na2Si2O5 formed in the slag may indicate a more stable
slag. Na2CO3 contents higher than 38 wt% decreased the antimony recovery
since it promotes the Na2Sb4O7 compound in the slag. The oxidation and
reduction process was modeled in FactSage 7.3 software for a better
understanding of the Na2CO3 and SiC additions on the antimony recovery rates
and compounds formed in the slag.
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