question_answer

  (a) Why can't alumina be reduced by carbon? (b) What is the role of depressant in froth floatation process? (c) Co which is better reducing agent for FeO? (i) In the lower part of blast furnace (higher temperature) (ii) In the upper part of blast furnace (lower temperature)                                                                              [3 x 1]

Answer:

  (a) When reduced with carbon, reaction is non-spontaneous since, Al has higher affinity for oxygen compared to than that of carbon. Thus, (alumina) cannot be reduced by carbon.                                                                [1] (b) Sometimes .depressants are used to prevent certain types of particles from forming the froth with the bubbles. NaCN is used as a depressants in the separation of ZnS and PbS. NaCN acts as a depressant for ZnS but does not prevent PbS from the formation of froth due to complex formation. in forth                                        [1] (c) (i) In lower part (higher temperature zone) C is oxidised to CO. (ii) In upper part (lower temperature zone) CO is a better reducing agent.                          [1]