charls1,

You have provided us nowhere near enough information to answer that question.

If your present motor worked, you need a new one just like it. Failing that, you need to get a mechanical engineer on your site.

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JHG

My field is fluid mixers, but I suspect solid powder mixers are similar - don't bolt a bigger motor or gearbox on the assembly unless you don't mind creating a failure somewhere else. Mixing equipment is typically sized for a mechanical load and if you increase those loads, everything could fail including its mounting / support structure. That gets very dangerous.

It sounds like you appreciate a fresh approach to sizing to reach a given process outcome. If you're limited to equipment you have on-hand, or want to try your luck with used machinery, give it a go. If you want a legitimate process calculation and sizing, a mixer manufacturer should be able to collect this information (and quite a bit more) to quote you a mixer that will certainly do the job.

For reference: commercially-available mixer with 500 L capacity (roughly 300 kg) requires 7.5 kW drive motor. Agitator speed is 1440 rpm. Gearbox, if any, changes motor speed to agitator speed. For this size, it would not be unusual for motor speed to be same as agitator speed (high torque squirrel cage induction motor operating on 50 Hz line frequency with approximately 4 percent slip).

Converting energy to motion for more than half a century

I'm hypothesizing that there is some sort of affinity law relationship that will apply - affinity laws

edit - see this on mixing also - no doubt there are better discussions