Since the commissioning of the Hamburg primary smelter (1972), it has been continuously optimized. The continuous optimization of the throughput capacity is contrasted by the trend of decreasing copper concentration and increasing complexity (bismuth (Bi), arsenic (As), lead (Pb), selenium (Se), tellurium (Te) and nickel (Ni)). Future optimizations will address the issue of minor element management to use synergies between metal production routes (copper, lead, zinc). In the context of this metallurgy, the importance of the elements As, Sb, Sn, Cu and Ni is addressed in terms of the formation of an intermetallic phase, called speiss. In this paper, by detailing the understanding of the feed formation mechanism in the lead electric furnace, the extent to which the properties of the products can be specifically influenced is explained. In this context, the investigations deal with specific questions on how to optimize the existing system in terms of selective extraction of arsenic, recovery of nickel and concentration of precious metals in the speiss. In order to study the chemical equilibrium between the matte-/speiss- and lead phases, an experimental setup was set up which includes the use of pre-melted material including the corresponding slag phase and allows the desired oxygen potential to be adjusted by supplying a CO/CO2 atmosphere. The influence of the oxygen partial pressure (log pO2) and the initial feed mixture variation on the speiss and matte composition were investigated and graphically represented. Four ratios (Pb/S, Pb/Cu, Cu/S, As/Ni) were defined for the feed material variation. For the chosen parameters, it was shown that copper-rich speiss are formed with decreasing oxygen partial pressure (log pO2 = -10 to log pO2 = -12) and with the increase of Cu/S-ration in feed material, which is disadvantageous for the extraction of arsenic, but beneficial for the collection of silver and gold. If the extraction of arsenic is to be improved, so-called true speiss must be aimed at. This is achieved by changing the feed material mix (Pb/Cu¿, Cu/S ¿). Arsenic plays a key role for effective copper/nickel separation. In real speiss, i.e. those with a high concentration of speiss forming agents (As+Sb+Sn), also show an increased nickel concentration and a targeted extraction via the speiss (lower nickel concentration in the copper lead matte phase). For the described context, the existing knowledge from the literature, thermodynamic calculations and operational experience could be summarized and extended by knowledge about additional operating windows. The data are used to optimize the lead electric furnace process operated at Aurubis AG, and the test setup developed act as the basis for carrying out further test series.