Minemakers did an Enabling Study comparing the base case...

Minemakers did an Enabling Study comparing the base case economics of the IHP and the Wet Acid Process for a 20 year mine life. This was announced 28/11/2011.

http://www.minemakers.com.au/documents/111128WonarahEnablingStudyConfirmsEconomicPotentialforMajorFertiliserProductionFacility.pdf

It shows a compelling case for IHP over WAP, and doesn't take into consideration the advantages that a scaling up of 1 kiln at a time has on initial funding requirements. Of course the BFS will determine more accurately the economics of IHP as its completed next year, but the back of the envelope figures you have produced Battlah show how compelling the projections are. One thing that improves that NPV you calculated is that the 181,000 tpa per kiln is just the contained P2O5, each kiln is capable of 259,000 tpa of 70% SPA, at $1000-$1200 per tonne. The Enabling Study in 2011 showed an Opex of about $400 per tonne, as you've noted costs will have changed which the BFS will reflect.