Removing floor tile cement from concrete subfloor

[shannyla]

So we're lifting a quarry tile floor in our kitchen to get the depth we need to add underfloor heating and insulation boarding onto the concrete slab. We're then going to lay new ceramic tiles over the top. We need the depth to avoid a step up from the hall. The quarry tiles are coming up easily enough, but are leaving a thick layer of tile cement on the slab.

My question is what is the best method to prepare the slab, is it a case of removing the cement to leave a smooth flat slab? That to me sounds like the best option but what is the best method of removing the cement? Would a floor scrabbler do the job (have never actually seen one...) or am I going to be chipping away for a while with a bolster..?

Any pointers much appreciated.