Abstarct: In this thesis, experimental and theoretical work on the pilot paste thickener for water recovery from copper tails and then concentrate of copper tails has been done. The Selected flocculant was Magnafloc 5250. For increasing sedimentation flux and better flocculation feed dilution was done until 10 mass percent. During the experimental tests the effect of various parameters such as, residence time of sedimentations, inlet and outlet tail rate and rake velocity was investigated. Mass solid percent of about 60% at paste discharge was The purpose of experimental tests, but in first series of experimental works it was not achieved (experiments of 1 to 3) and discharge solid percent was about 50%, The first impression by the team was that low amount of solid percent at discharge was because of variations at inlet to thickener, this opinion was rejected in the next series of experiments because the feed rate in experiment 3 was regular but there was no improving in discharge solid percent. Finally troubleshooting showed that the reason for the low amount of discharge solid percent was related to the fine solid particle distribution that reduced permeability of sedimentations. With correction in the feed system of pilot thickener from experiment 4, the problem was fixed and the solid discharge mass percentage reaches to 60%. Thus, baxsed on experiments on pilot paste thickener and solid particle size distribution, a relation for discharge solid percent and the specific surface (that is related to particle size distribution) in some heights of mud was suggested . Other result of experimental works in flocculation field was that flocculant dose is related to particle size distribution, environmental temperature, flocculant and tail type. because collision between particles and between particles with eddies that contain flocculant is related to particles size. Thus, in experiments that particle size distribution was very fine, there was flocculant waste from the weir in the recovered water .During the experiments, yield stress of copper paste in various solid percent has been measured by slump test at discharge section of pilot thickener pastes and the help of lump model. One phase and two phase (VOF) model numerical simulation of Feedwell was performed using the CFD software. Both models showed that the feedwell of pilot paste thickener doesn’t work at optimum state and it has been shown that with changing in feedwell geometry specially feedwell inlet pipe diameter and inlet pipe degree, feedwell can work in a better state. The effects of other parameters such as rake shaft rotation velocity and tail inlet flow rate were investigated. The results indicated that the rake shaft Rotation, doesn’t have important effect on feedwell performance because the rotational velocity of shaft is very slow, and increasing the capacity of pilot paste thickener is possible