The world’s two largest mining companies are planning to raise capital expenditure from decade lows as a firming rebound in commodity prices paves the way for at least $12-billion of growth projects. BHP Billiton Ltd., the No. 1 miner, expects to raise spending by 15% in fiscal 2018, while Rio Tinto Group forecasts it will boost expenditure from next calendar year. Melbourne-based BHP is looking to approve about $4.7-billion of investments for a oil venture in the Gulf of Mexico and a copper project in Chile.