A bit early to speculate as there are many moving parts to this.
They will be working from base case assumptions for example about the sale price of 99% TiO2 and 99% pure hematite. Typically these spread sheets set the price well under spot prices if they are at all elevated. The engineering consultants wouldn't put their name to it if they are not conservative.
There are also a dozen points along the flow sheet which could be tinkered with for example with the acid regeneration. Current flash regeneration gives 98-100% recylcing but it is energy intensive. The current costs are likely to have been done on the old standard "pickling plant" process which is 50-60 year old and energy intensive. There is a newer hydro process which uses less heat and use hemical reagents to drop out the metals. No idea of the cost, but likely to be perhaps 20% cheaper given the cost of gas in remote regions.
SPM Price at posting:
19.0¢ Sentiment: LT Buy Disclosure: Held