Abstract: A method and apparatus for determining electrochemically active components in a process stream. The method comprises the steps of providing a sample in which the components are contained, and depositing the components onto a working electrode, altering the environment of the working electrode so that it is immersed in a supporting electrolyte by effecting a matrix exchange and stripping the deposited electrochemically active components from the working electrode into the supporting electrolyte. The method and apparatus utilize a measurement cell which comprises a vessel (10) for containing the supporting electrolyte and a mercury drop electrode (150).

Abstract: A process for treatment of an acidic solution containing ferric iron and at least one non-ferrous metal, prior to removal of ferric iron therefrom, is characterized by adding a specified amount of at least one neutralizing agent, and separating off from the solution any residue or undissolved neutralizing agent remaining after neutralization, thereby producing a solution possessing an acid consuming capacity termed "negative acidity", and still containing substantially all the dissolved ferric iron in solution, and from which ferric iron can subsequently be removed with the generation of less acid compared to that generated from solutions partially neutralized according to the prior art.

Abstract: A process for controlling the water balance and the concentration of impurities in an electrolytic zinc plant circuit with which is operated at least one selective zinc precipitation (SZP) process plant which comprises one or more of the steps(a) a two-stage SZP process plant in which a compound containing calcium carbonate is used in the first-stage to precipitate portion of the zinc in incoming solution, and a compound R containing zinc oxide, preferably calcined zinc sulphide concentrate, is used to precipitate most of the remaining zinc;(b) displacement of the zinc depleted solution associated with solids leaving the SZP process plant by solution drawn from the electrolytic zinc plant circuit, and(c) use of a compound R with a particular average particle size.

Abstract: A process for precipitating iron as a jarosite from a sulphate solution containing ferric iron, free acid and valuable non-ferrous metals, characterized by cooling the solution; partially neutralizing the free acidity, and then clarifying the solution; heating the clarified solution to a temperature not exceeding the boiling point at atmospheric pressure, in the presence of at least one ion selected from the group consisting of sodium, potassium and ammonium ions, and in the presence of recycled jarosite, and without the addition of any further neutralizing agent, so that substantially all of the ferric iron is precipitated as a jarosite; and separating precipitated jarosite from the solution; thereby producing a jarosite contaminated with only minor amounts of non-ferrous metals, and a solution which may be further processed by established procedures for the recovery of dissolved valuable non-ferrous metals therefrom. The invention also contemplates a dilution step, and recycle of jarosite.

Abstract: A process for treatment of lead residues, without prior sintering, in which residues more than 70% of the lead is present as lead sulphates, comprising addition of the said residues, together with a reductant containing carbon and together with fluxes that will react to provide a slag containing FeO, CaO and SiO.sub.2, directly to an electric furnace operating at a temperature of 1000 to 1500.degree. C in the slag layer to produce in the furnace a lead bullion. The expression "lead sulphates" will be understood to include lead sulphate and other compounds containing lead and the sulphate ion, for example, the basic lead sulphates.