DC High Current Power Supply for Electrochemical Plant
A silicon-controlled rectifier (SCR) is a type of thyristor. Another type of thyristors is the Gate turn-off thyristor (GTO). 

A diode base rectifier is called an uncontrolled rectifier. With the use of SCRs (among other devices) you get a controlled rectifier. The benefits of a controlled rectifier is that you can control the load voltage and power factor. Thyristor rectifiers are the most common solution for this kind of application (electrowinning).

If you want to stay with diodes, then you're looking at devices like these ones. In the case of thyristors, then these ones.

Regarding capacitors, you would need to design your own capacitor bank.

By the way, 5V at 50 kA means 250 kW, for this kind of power one normally has to take into consideration the generation of harmonics and reactive power consumption, since utilities normally impose penalties for harmonics and reactive power consumption above certain limits. You might want to look at 12-pulse rectifiers.