Input / Output error while copying files

I am having problems with an external WD 500 GB hard drive.

The drive has 2 partitions, #1: 184 GB, #2: 315 GB

Partion 1 does not mout (even with DU), however most of the important data is on partion #2

I am able to recover part of the files using the copy command on Terminal.

however, many of the files can't be copied due to an input/output error, and these files end up as zero bites files on the target disk (the correct size shows on the source disk though)

I also trying copying the problem files individualy with the same results (zero bytes and input/output error).

I think the problem may be due to bad sectors on the external drive, but I don't have any idea on how to fix it.

I wonder if deleting from the source drive those files already copied to the target drive and moving the problematic files to another directory may help to solve the problem.

Is there any Terminal command to move files from bad sectors to good sectors?

Thanks!