Copper recovery from a leach residue: CCD washing + hydroxide precipitation

A leach residue leaves a heap/tank-leach circuit as a slurry — insoluble gangue solids carrying entrained copper-sulfate pregnant liquor that would be lost to tailings if simply thickened. A counter-current-decantation (CCD) wash train recovers it: the residue is washed with clean water flowing counter-current to the solids across a chain of thickeners, so the dissolved copper is displaced into a pregnant-liquor overflow while the washed solids go to tailings. The new ccd_washer unit op models the whole train in one block via the classic counter-current washing equation f = (R-1)/(R^(N+1)-1) (Perry's §18; Coulson & Richardson Vol. 2): five stages at a wash ratio near 4 recover ~99.9% of the dissolved copper, leaving only ~0.08% with the tailings. The pregnant liquor is then dosed to pH 8, where the copper drops as Cu(OH)2 sludge (the precipitator op on the CRC-cited solubility-product chemistry), leaving a barren raffinate for recycle. Honesty notes: ideal equilibrium washing (perfect mixing + constant underflow at every stage; no settling-flux / thickener-area sizing, wash-water short-circuiting or solute adsorption on the solids) and equilibrium Ksp precipitation at a dosed pH (B-dot activity, a dilute-liquor solution-volume estimate) — a screening process-design starting point, the metallurgical-balance level, not a certified settling/reagent deliverable.