In the extraction of tungsten metal, WO3 is reduced with hydrogen gas . Why is it not advisable to use carbon for the reduction?

Tungsten is found in the form of tungstate , the chief ores being Wolframite (FeWO4 and MnPO4) , schelite( CaWO4) and stolzite ( PbWO4) . The small amounts of MoS2 in the ores are concentrated by the foam floatation process . This is converted to WO3 . It is reduced to metal with hydrogen, reduction with carbon should be avoided because it forms carbide instead of metals .

Tungsten ores are concentrated by mechanical and magnetic process and the concentration attacked by fusion with NaOH . The cooled melts are leached with water, giving solutions of sodium tungstate from which hydrous WO3 is precipitated on acidification. The hydrous oxide is dried and reduced to metal by hydrogen.