excise duty on loan material

my client is running  manufacturing unit and goods are excisable. he has got orders from  govt owned unit. the required raw materials was not available in the market. hence the purchaser has given raw materials with payment of excise duty simply sent  thro delivery challan. now  my client has to return the loan material.  the purchaser is not ready to pay the excise duty.  whether my client can sent the materials (excisable) with out payment of excise duty. pl clarify.