Method of washing gas in two stages using precipitation of sulfide and alkaline absorption

A method of washing hydrogen sulfide and carbon dioxide from a gas obtainable by gasification of carbonaceous biomaterial, said method comprising: a. contacting said gas with a first absorbent solution comprising ions of transition metals, said transition metals selected from copper, zinc, iron and cobalt and mixtures thereof, in aqueous acidic solution; b. joining hydrogen sulfide to said first absorbent solution; c. recovering the gas of step b; d. contacting the gas recovered from step c with a second absorbent solution comprising an absorbent alkali; and. bind carbon dioxide to said second absorbent solution; and f. recovering the washed gas from step e.