Usually one container can hold about 28T of copper cathodes...

Usually one container can hold about 28T of copper cathodes stacked into 4T stacks,
@ 20,000 tonnes of copper plate made on site per year divided by 28T per TEU container would need about 714 containers to load, truck and ship.

Another cheaper option about copper cathode made on site it can be trucked to closest port in bulk, stockpiled then loaded bulk into a hatch of a bulk carrier say about 10K to 20K tonne of plates in 1 shipment and not even need to use containers or ship as a combination of both. What ever works best i guess with cash flow requirements and rate of plate made on site. Could be a number of trucks transporting everyday to port, i am not sure of how much they make at a time tho and how long yet.