Characterization and Potential Application of Bromelain from Pineapple (Ananas comosus) Waste (Peel) in Recovery of Silver from X-Ray Films

Bromelain is a proteolytic enzyme, which is predominately found in all parts of a pineapple plant (Ananas comosus). It has immense application in the pharmaceutical industry as well as in food, cosmetic, and leather industries. However, bromelain from pineapple fruit peels is a less explored source for making valuable products. Therefore, the objective of this study was to characterize and investigate the potential application of bromelain enzyme extracted from pineapple juice processing waste peels in gelatin hydrolysis and removal of silver from X-ray films. Extraction of bromelain was performed with a 1 : 2 ratio (w/v) of the extraction mix, pineapple fruit peel, in phosphate buffer (pH = 7.0). The activity of a crude enzyme was 7.2 U/ml, and it was active in a broad range of pH (2.5–12) and temperature (25–85°C) without losing its activity. This implies that the enzyme is heat tolerant. The optimum temperature and pH of the enzyme were recorded at 70°C and pH 7.0, respectively. At optimum conditions (70°C and pH 7.0), complete hydrolysis of the gelatin layer from X-ray film was observed at 30 and 34 seconds, respectively. The enzyme was repeatedly used more than 50 times without significant loss of its activity. Using a minimum concentration of bromelain (3 ml = 21.6 U) along with phosphate buffer (37 ml), it is possible completely to remove gelatin within 210 seconds. The properties of the enzyme showed that it has promising potential industrial applications for repeated utilization of the enzyme in both silver recovery and recycling of the X-ray film base.

Fine Silver Powders Production

The article lays out the findings aimed to develop the fine silver powder production technique for electronics industry by selecting the variable parameters whereby a number of powder grades can be produced in the existing production environment (JSC “Uralelektromed”, Russia). The tests for significance of the parameters of silver recovery by ascorbic acid such as pH level of nitrate silver solution, dispersant flow rate, initial concentration of silver, mixing rate and solution temperature made it possible to choose optimum conditions to produce powders of 0.8-6.3 μm in particle size, of 3.0-4.2 g/cm3 in tapped density and with the specific surface area of 2300-4300 cm2/g. Crystalline silver of 99.98 % purity served as a raw material for obtaining silver powders.

Electrochemical Recovery of Silver Using a Simple Cell

The amount of generated e-waste during the last decades has been steadily raising to the point at which it is highly desirable to obtain the precious metals by recycling the e-waste without the need of exploiting the environment. The rapid development of technology, steep growth of modern facilities with user-friendly electronical devices and a stiff competition between manufacturers are among the main reasons for decreasing the life span of such devices, and subsequently end up as an obsolete waste product. Rapid industrialization and urbanization have also caused many environmental problems, e.g. heavy metal contamination. Silver is one of the precious metals with exceptionally high industrial applications, which makes it an area of research of high interest. Demand for silver continues to grow with progress in the industrialized world, while the world reserves of high-quality silver ores are declining. Although, there are large stocks of low and lean quality silver ores still to be mined, the main goal of this article is to provide a simple, effective and eco-friendly method of silver recovery from e-waste, e.g. electrical circuit breakers using an electrochemical cell. After 20.75 days of the experiment, 1481.5 grams of silver contacts were processed with a final yield of 61.41 % grams of silver dendrite crystals (99.9 % purity).