Large quantities of CO

2

and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO

2

emission reduction and comprehensive utilization of the solid waste. This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace (TBBF) slag

in which the TBBF slag is roasted with recyclable (NH

4

)

2

SO

4

(AS) at low temperatures and converted into the sulphates of various valuable metals

including calcium

magnesium

aluminium and titanium. High value added Ti-and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH

3

produced during the roasting is used to capture CO

2

from flue gases. The NH

4

HCO

3

and (NH

4

)

2

CO

3

thus obtained are used to carbonate the CaSO

4

-containing leaching residue and MgSO

4

-rich leaching solution

respectively. In this study

the process parameters and efficiency for the roasting

carbonation

and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium

magnesium

titanium and aluminium reached 92.6%

87% and 84.4%

respectively

after roasting at an AS-to-TBBF slag mass ratio of 2:1 and 350℃ for 2 h. The leaching solution was subjected to hydrolysis at 102℃ for 4 h with a Ti hydrolysis ratio of 95.7%and the purity of TiO

2

in the calcined hydrolysate reached 98 wt%. 99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH

3

. The carbonation products of Ca and Mg were CaCO

3

and (NH

4

)

2

Mg(CO

3

)

2

·4H

2

O

respectively. The latter can be decomposed into MgCO

3

at 100-200℃ with simultaneous recovery of the NH

3

for reuse. In this process

approximately 82.1% of Ca and 84.2% of Mg in the TBBF slag were transformed into stable carbonates and the total CO

2

sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO

2

obtained can be used directly as an end product

while the Al-rich precipitate and the two carbonation products can act

respectively

as raw materials for electrolytic aluminium

cement and light magnesium carbonate production for the replacement of natural resources.