Study On The Recovery And Enrichment Of Nickel From Indonesia Limonitic Laterite By Reduction Roasting-Magnetic Separation

Currently,most of the global nickel production originated from nickel laterite resources.Indonesia has the largest nickel reserves with 21million metric tons of nickel ores which are predominantly laterite-type（limonitic&saprolitic）.The limonitic nickel laterite in Indonesia is still not utilized much due to its lower nickel grade than saprolitic.The currently available route is through the High Pressure Acid Leaching process（HPAL）,which is expensive and produces a large volume of waste.Recently,the reduction roasting-magnetic separation process has been studied to upgrade limonitic laterites.In the current study,the beneficiation of Indonesia’s（Bahodopi）limonitic laterites through reduction roasting–magnetic separation with various sulfate-based additives(K₂SO₄,Na₂SO_4,and Ca SO₄)is explored.The effect of various parameters such as roasting temperature,roasting time,magnetic strength,reductant dosage,additive dosage,and additive type on the nickel-iron grade and recovery were investigated.The main results achieved were:（1）In the reduction roasting-magnetic separation test on the Bahodopi’s limonitic laterite（1.33%Ni,50.10%Fe）without additive,the highest nickel and iron grades obtained are 1.93%and 70.44%,respectively（T=1000°C,reductant dosage=20wt%,t=120 minutes,magnetic strength=2000 Gauss）,while the highest nickel and iron recovery are 87.48%and 86.12%respectively（T=1000°C,reductant dosage=10wt%,t=60 minutes,magnetic strength=2000 Gauss）.Generally,increasing the roasting temperature and reductant dosage,correlated with increasing nickel and iron grade,as well as nickel and iron recovery.Prolonging roasting time will increase nickel and iron grade,but reduce the nickel and iron recovery.Meanwhile,increasing the magnetic strength has little effect on the nickel and iron grade,but increases nickel and iron recovery.The relatively equal recovery of iron and nickel,as well as the high Fe/Ni ratio（>36）,indicate that the overall reduction roasting-magnetic separation process still has low selectivity.The amount of magnetic concentrate recovered was still high（percent concentrate>80%feed）,indicating that the separation from the gangue was inefficient.This may be contributed by the occurrence of magnetite,which is the dominant phase,as shown in the XRD data from temperature variation.The formation of magnetite could magnetize most of the feed,resulting in the more challenging separation using a magnetic separator.（2）The effect of various sulfate-based additives types and dosage on the performance of reduction roasting-magnetic separation were investigated.The first experimental results in lower nickel and iron grades,which is unexpected,as the additives typically increase the nickel grade by suppressing the iron recovery.Therefore,some technical modifications were made to obtain improved results.The three types of additives（K₂SO₄,Ca SO₄,and Na₂SO₄）increase the nickel grade and decreases the nickel and iron recovery along with the increasing dosage.Based on the highest nickel grade,the optimum dosage for the three types of additives is 15%,whereas to obtain the highest nickel and iron recovery 5%dosage of additive is preferred.The highest nickel grade obtained was 2.40%with 81.13%nickel recovery,while the iron grade obtained was 71.81%with 64.44%recovery using 15%Na₂SO₄.The performance of the additives based on the highest nickel grade obtained is in the following order Na₂SO₄>K₂SO₄>Ca SO₄.Overall,Na₂SO₄ addition achieved the highest nickel grade and recovery,and lowest iron recovery in 15%dosage compared with other additives in the same dosage.（3）The effects of roasting temperature,additive dosage,and additive type on the mineralogy phase transformation during the reduction of limonitic laterite were investigated.The temperature has transformed goethite from the raw ore into magnetite,hematite,wustite,and ferronickel phase.Magnetite and hematite are observed in all the temperature ranges.Meanwhile,ferronickel is only observed when the temperature is above900°C,and wustite is only observed when the temperature is 1000°C.The available phases in the variation of additive dosage are wustite,ferronickel,troilite,and megakalsilite phase.The addition of K₂SO₄ results in the occurrence of new phase troilite and megakalsilite,and the disappearance of magnetite and hematite phase.The increasing K₂SO₄ dosage has increased the Fe O intensity and decreased Fe Ni and Fe S intensity.Formation of Fe S layer inhibits Fe O contact with reductant,thus reducing Fe Ni generated.The decreasing iron recovery will result in a higher nickel grade in the final concentrate.The occurrence of megakalsilite（KAl Si O₄）,Ca₃Si O₅,and nepheline（Na Al Si O₄）is observed in the XRD pattern of reduced ore when 15wt%of K₂SO₄,Ca SO₄,and Na₂SO₄ was added respectively alongside Fe O,Fe S,and Fe Ni phase.The high melting temperature of these silicate species（KAl Si O₄=1750°C,Ca₃Si O₅=1900°C,Na Al Si O₄=1525°C）observed in this experiment means the upgrading mechanism may work only through sulfidation of Fe O into Fe S.The relatively low Fe S intensity and the absence of low melting point silicate species may explain the lower nickel grades obtained in this study compared to the other studies.44 graphs,9 tables are included,and 83 references are cited in this dissertation.