1. Determine your batch residence time at the given solids content, measure the pulp density (initial, final);
2. Calculate the required total reactor volume for continuous test V(L) =  R(h)*F(L/h), apply the required safety factor (1.2 minimum, more if heavy frothing);
3. Decide on the number of tanks, use baffles, test mixers with water, use decent diameter down-comers, reach to the bottom best, design carefully around this detail.

Good luck.

Thank you rheomet for the response.

Building on what Rheomet provided - In the ultimate design the number of tanks should not be less than 2 and ideally 4 or more to make sure that you minimize short circuiting.

I have done a lot of stirred tank leach tests at lab scale using nothing more than a mixer in a 1 liter beaker with good results, baffles are nice to have but not necessary if you can keep everything in suspension with mixer speed. 

Keep in mind that in a pilot plant it is good try and mimic the final plant design as closely as possible so that scale up issues are decreased.  Cascade or overflow is hard at the pilot scale if the tanks are small (<20 l) due to the fact that small overflows tend to not work well.  I have used peristaltic pumps in between stages to transfer slurry in batches down the line - can be manually controlled. 

Hope this helps.

Thanks Todd. I have also observed that material gets stuck behind the baffles. Which makes me wonder if they're really that relevant if you can achieve a perfect solid suspension. The idea of using pump for slurry transfer looks good and i'll definitely consider it. Thank you