On the Internet, one can find a number of firms that dispose of computer parts and guarantee that they will be wiped of all data, and/or reused where possible, and disposed of safely.
A motherboard often contains what is termed "digger gold" small amounts of precious metals which can be recovered by soaking the boards and electrical components first in nitric acid (it dissolves the silver) and then in aqua regia, which gets the gold. The process may be marginally cost effective because of the cost of disposal of the acids, but the article I saw was written when Gold was $100 per troy oz. Today, the prices for precious metals may make the processes more attractive and financially viable.
Search the web for "e-wastes" and for computer recycling. I'm sure you will find what you need. As far as separating the wastes, that has to be done at the office by putting bins up for electronic parts and training personnel to segregate. It's not economical to try and do it after the waste gets mixed with the trash.