Formulation of fish feed using essential elements from platinum minerals tailings and groundnut oil processing waste: A circular economy initiative.

Abstract

The high cost of imported fish feed ingredients in Zimbabwe has become a concern. Given that fish feed primarily consists of essential elements and proteins, this study explored the potential of platinum mineral tailings, an underutilized byproduct of ore flotation, as a source of essential elements for fish feed formulation. Platinum mineral tailings may cause negative environmental effects through acid drainage caused by uncontrolled leaching of elements. The platinum mineral tailings were characterized using X-ray fluorescence (XRF) and X-ray Diffraction (XRD) to determine their elemental and mineralogical composition, respectively. XRF revealed the presence of Fe, Ca, Si, Mg and Cr. XRD results concurred with the XRF analysis showing key mineral phases including taenite, pyroxene, landauite, enstatite ferro and kyanite. To recover essential elements, comparative leaching studies were carried out using inorganic acids 0.5 M sulfuric, hydrochloric, and organic acids: acetic, and citric acids. Citric acid exhibited higher extraction efficiencies compared to acetic acid. A combination of 0.5 M acetic acid and 0.5 M citric acid was used in the ratio 1:1 to improve extraction efficiency. Optimization studies were carried out using response surface methodology to determine the effects of contact time, acid concentration, temperature and pH. The optimized conditions were pH = 2, contact time = 5 hrs, and a temperature of 70 °C. The resultant leachates were analyzed using Inductive Coupled Plasma- Optical Emission Spectroscopy (ICP-OES). ICP-OES showed percentage recoveries of Ca (42. 42 %) , Cu (0.97 %) , Fe (0.05 %), K (45.61 %), Mg (35.48 %) ,Mn (27.43 %) , Na (64.42 %) and Zn (16.62 %). The leachates were then combined with groundnut oil processing waste. Groundnut oil processing waste was used as both an organic binder for the extracted elements, as well as a source of protein for the formulation. The resultant mixture was processed into pellets using optimized parameters of a volume of 25 ml of the mineral solution, 37.5 g of groundnut oil processing waste with 11% moisture content. The proximate and elemental analysis produced the nutritional content (%) as carbohydrates (56.6 ± 0.38) , protein (10.79 ± 0.12), lipids (15.91± 0.05) , ash (4.26 ± 0.10) , fiber (2.18 ± 0.04) and moisture (9.07 ± 0.05). Elemental concentrations (mg/kg) were, Ca (961.49 ± 0.46) , Cu (6.54 ± 0.069) , Fe (79.71 ± 0.29), K (5118.06 ± 1.4) , Mg (1090.10 ± 0.49), Mn (6.46 ± 0.061), Na (1183.07 ± 0.81) and Zn (0.296 ± 0.0029). iv

The results showed potential of using waste from from metallurgical processing of platinum mineral as a source of essential elements combined with waste of processing oil from a local available indigenous crop Arachis hypogaea (groundnut). These are cheap to obtain as they are local however cost arise from purification and analysis to ascertain safety and quality. This study validates the technical feasibility of extracting elements from platinum mining waste for use as nutritionally essential elements to enrich groundnut oil processing waste. Comprehensive analytical characterisation and formulation optimisation were carried out. The results demonstrated nutrient recovery efficiency, toxic element removal, providing the essential baseline data required for designing further research on safety assessments, in vivo feeding trials and economic feasibility assessments.This approach has potential to offer a sustainable, locally sourced alternative to conventional feed ingredients, contributing to waste valorization and economic resilience in Zimbabwean aquaculture.