Crystallization and deposit formation of lead sulfide from aqueous solutions

Once-through pipe flow experiments were employed to determine PbS deposition rates on metal surfaces. Parallel tests to characterize the PbS sols facilitate data interpretation. It is established that lead sulfide deposition occurs within a relatively narrow pH range, related to PbS solubility. The curve of initial deposition rate versus pH has a 'bell' shape, being almost symmetric about the 'threshold' pH of spontaneous bulk precipitation. Nucleation and subsequent crystal growth right onto the substrate occur below the threshold pH, leading to hard deposits. With increasing pH above the threshold, deposition of crystallites from the bulk appears to gradually dominate, leading to the formation of loose deposits. The deposition rate increases with flow rate, PbS concentration, and temperature, while increased salinity and temperature cause a shift of the deposition curve toward higher pH values.