Removing limesale from a concrete kitchen top

[opps]

I double-checked and the recommendation is in fact to use an orbital sander with diamond polishing pads. Although I've seen videos recomending polishing with a grinder with diamond polishing pad, my concrete countertop guy says a grinder goes too fast and will throw too much water around. Orbital sander is okay apart when polishing the kitchen island where I've got a hob that's proud of the concrete countertop. I've yet to resolve that but I'll update upon clarification.

I had a look for polishers and found this one.
It looks good and doesn't cost an arm and a leg.

Your link is bad I suspect you mean a DA sander such as

18V XR® Brushless 125mm Dual Action Polisher - Tool Only

The DCM848 18V dual action polisher is the perfect cordless solution for polishing applications powered by a powerful brushless motor to prevent stalling in heavy use. To achieve the best finish possible the DCM848 features a free rotating drive to stop the pad when too much pressure is applied...

www.dewalt.co.uk

Rather than just spinning, it oscillates as it spins (AKA random orbital). It reduces the risk of circular score marks.

Apropos the hob you can wrap some tape around a wide taping knife and sand up to it, moving the knife as required.

EG https://www.toolstation.com/marshalltown-qlt-blue-steel-taping-knife/p21844

The knife will prevent the DA from hitting the edge of the raised hob.

If you are concerned that you might inadvertently hit the silicone seal, you can use cardboard/etc to pack out the back of the knife.

I have a couple of DA sanders but they are too slow for polishing. Additionally, because of the dust extraction, they cannot be used with water.