The Study of the Formation of Sodium Chromate from El-Baramiya High-Silica Chromite Ore Concentrate Using Hydrated Lime

Abstract

The formation of sodium chromate from a mixture of high-silica chromite ore concentrate (48.8%), soda ash and hydrated lime was investigated. Hydrated lime was added to an optimal mixture of Cr2O3:Na2CO3 (mole ratio 1:2.5) (mole ratio of CaO 0-3) and the materials were roasted at 1000°C for 60 min and PO2 0.21 atm. Results revealed a significant decrease in sodium chromate yield (from 42% to 25%) as the (CaO/Cr2O3) mole ratio increased from 0-0.5. Increasing the (CaO/Cr2O3) mole ratio above 1.0, an optimal chromate yield of 70% was achieved at the mole ratio of 2.5. In addition, roasting of optimal mixtures of soda ash, chromite ore and hydrated lime (CaO) (mole ratio 2.5:1:2.5) within the temperature range of (900-1000 °C) provided a maximum chromate yield of 92% at 1000 °C after 2 hours. Overall, the data revealed that while the hydrated lime addition significantly increased the reaction product yield, it also increased the process energy of activation from 112 kJ/mole for the Na2CO3:Cr2O3 (mole ratio 2.5:1) mixture to 171.6 kJ/mole during roasting time (40-100 minutes).