• Energy Research

Aluminium, iron and plastic are materials which are extensively used at both industry and individual levels. However, significant amounts of aluminium, iron and plastic end up in the environment. Specifically, bottle caps made of these materials are often thrown away, with or without bottles, and appear among the common plastic debris entering the world’s oceans and beaches. More than 20 million bottle caps and lids have been identified during beach-cleaning campaigns over the last 30 years. To recover bottle caps from the shores, conventional technologies can be used. In this paper, the physical properties of used metal and plastic bottle caps were examined and related to the settling and rising velocities of the caps, as well as their drag coefficients and hydrodynamic modes in water environments, with respect to gravity separation. The sample contained aluminium, iron, high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) bottle caps. The findings revealed that the density differences between the bottle caps resulted in the terminal settling velocities of aluminium and iron particles, which were significantly higher than the rising velocities of the plastic caps. The results allowed us to design a flowsheet for bottle cap recovery from beach coasts in order to reduce environmental impact and produce add-on plastic and metal products.

Mining and mineral processing industry adversely affects ecosystems and communities in nearby areas, including high freshwater consumption and scarcity. That is why the emerging global trend is to use sea water in flotation to recover valuable minerals from finely disseminated base metals ores. Recent studies investigate sea water flotation of copper, molybdenum, nickel sulphides and pyrite, while flotation of sphalerite, the main valuable mineral for zinc production, remains uncovered. This paper examines the feasibility of sphalerite flotation by conventional collectors in artificial sea water using a bubble-particles technique and frothless flotation tests. Potassium isopropyl xanthate (PIPX) and sodium isopropyl dithiophosphate (SIDTP) were used as collectors, and copper sulphate was introduced as the activator, while zinc sulphate and sodium sulphide were used as depressants. We examined the most common size fractions of sphalerite: medium (−74 + 44 μm) and fines (−44 μm). The findings showed the feasibility of sphalerite flotation in artificial sea water. We also established correlations between the rate of bubble-particle attachment and the sphalerite flotation recovery resulting in the growth of flotation recovery with the increase of the bubble-particle attachment rate. The results can be used as guidelines in choosing flotation reagents for sphalerite flotation in sea water. Another practical application of the results is the potential for sustainable development of the industrial sector, ecosystems and societies due to the replacement of fresh water by sea water, although further technological and environmental studies are required.