Model: four stages in series, each a stirred hold-up dw_i/dt = in_i - w_i/tau_i with a fixed fraction R_i of the outflow passing on and the rest lost to residues. Steady state: product rate = F · g · f · R1R2R3R4 / x. Lumped first-order stages with constant recoveries: the numbers illustrate a mass balance, they are not plant data.

Alkaline leach: tellurides are oxidised to tellurite, Cu2Te + 2 NaOH + 2 O2 -> ...Na2TeO3; the leached fraction follows R1 = 0.97(1 - e^(-c/35)) with NaOH concentration c. TeO2 is amphoteric: neutralising to pH about 5.5 precipitates it (Na2TeO3 + H2SO4 -> TeO2 + Na2SO4 + H2O), overshooting redissolves part of it (R3 0.97 vs 0.86). Electrowinning obeys Faraday: m = I t M / (z F), z = 4.

Honest limits: constant recoveries, no selenium or copper balance, no cell voltage or energy model.