The largest uranium operation (Key Lake : Cameco) in the world routinely deals with As and Ni impurities and blends 'waste materials' containing Ni and As from the old Key Lake mining operation with McArthur River ore (20% U) to achieve a 4% U feed grade for processing using conventional technology.

As and Ni, along with other impurities, are separated from uranium during solvent extraction and then fixed in a separate operation to produce environmentally acceptable waste products for deposition.

I would suggest that you look up their publications - indeed the Metallurgy Manger undertook a thesis on this technology, so it should be available on-line.

Arsenic is relatively easy to fix as an inert solid - scorodite (iron arsenate) - the product made by bioleaching of gold bearing arsenopyrite ores.

As for fixing nickel, nothing readily comes to mind - but I am sure that someone will have a good handle on this.

Going back to basics, what is the nature of the nickel and arsenic mineralogy? Are they located in the same mineral vs. gersdorffite?

Some mineral processing (flotation - it has similar properties to pentlandite) may be a useful solution to remove the nickel and arsenic before you start leaching. 

The structure of the particular mineral must be studied and known and also flotation is one of the best processes to do that work.

I agree that if you have arsenic-sulfide minerals then flotation is the ideal way to go. In South Africa at a gold-uranium mine we pre-floated then burnt the flotation concentrate to produce the acid for uranium leaching.

Please note that the mining and processing (grinding & thickening of the slurry) take place in Under Ground (UG) and the slurry will pump to surface for transporting to the Mill. There is no space in UG.

There is no processing separation underground - i.e. metal extraction...so there would be enough room on the surface to install any processing solutions.