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Abstract
The extraction of silver metal from hospital x-ray films obtained from Life clinic Bori, was extracted using chemical precipitation method with different concentrations of sodium hydroxide as extractant and sodium sulphide as a precipitating agent. The x-ray films were washed with distilled water and wiped with cotton wool impregnated with ethanol and dried at 600C for 32minutes in oven. The x-ray films were cut into 4cm by 5cm. 140grams of the cut x-ray films were weighed and put into beakers labeled V, W, X, Yand Z containing 300ml 0.5M, 1.0M, 1.5M, 2.0M and 2.5M concentration of sodium hydroxide and heated for57minutes at 450C in water both with a continuous stirring, and also 150ml molar equivalent of sodium sulphide were added to each beaker to form precipitate. The supernatant was decanted and the wet precipitate was put in a graphite crucible and heated at 4000C for 25minutes using a furnace, and allowed to cool for 32minutes. Thereafter, the solid silver recovered was weighed again. The extracts obtained were digested and its silver ion content was estimated using Atomic Absorption Spectrophotometer(AAS). The estimated silver ion content value in each of the beakers labeled V (804.0 mg/kg of Ag), W (36,957.3 mg/kg of Ag), X (34,713.5 mg/kg of Ag), Y (28,854.9 mg/kg of Ag) and Z (28,188.8 mg/kg of Ag) were obtained respectively. This results obtained implies that beaker W has the highest amount of silver ion concentration, followed by beaker X, Y, Z and V as compared respectively.
CHAPTER 1
INTRODUCTION
1.1 Background of the Study
Silver is regarded as one of the noble and precious metals used for so many purposes especially in the photographic industry (Shankar et al, 2010). The waste x-ray films containing black metallic silver,in a gelatin nature is a very good source for silver recovery compared to other types of films. The quantity of silver in the x-ray films varies between 1.5 and 2.0% (w/w) according to Shankar et al., (2010). It has been reported that 5% of the world’s silver needs are supplied by recycling, out of which 75% is gotten from photographic waste (Shankar et al., 2010). With an increasing demand for silver in the world at large, recent attention is focus on x-ray films as one of the secondary sources of silver owing to the consideration of the amount of silver present in them (Hill et al., 2010).
Silver has been seen as a metal of a great commercial importance used in high strength and corrosion resistance alloys including jewelry. Due to its excellent properties, electrical, thermal conductivity and ductility, silver has been applied in aerospace, communications, chemical industry, medical equipment, electroplating, photographic materials and electronic industries at large (Mulongo et al., 2010). For decades, the medical sectors and films industries extensively use a very high quality photographic films and x-ray films where both of them depend much heavily on silver itself. Silver is a very unique metals that has a light sensitive materials capable of producing photographic images due to the shinning qualities of silver. The cost of silver has increased in recent times due to sudden price increase on the international market coupled with a world of shortage of silver (Khunprasert et al., 2008). Luckily, greater percent of the silver used by the photographic industries and hospitals for x-ray machine can equally be recovered from the photographic wastes which comprises of the x-ray films containing high concentration of dissolved silver and the chemicals such as sulfates and nitrates (Jeyaseclan and Sathananthan 1997).
Fifty present of silver produced is used in photographic and imaging materials. Silver is unique due to its Ability to react with light to produce images in applications like in photography and radiography (x-rays). Major emission of silver to the environments is from the manufacture and disposal of certain photographic and x-ray films in general (Adani et al., 2005). Silver is seen as one of the metals referred to as`coinage metal’. Its natural source is from the sulphide ore, silver sulphide (Argentite). The main uses of silver include the photographic industries, jewelries making and ornaments as well as batteries and image mirrors. Recycling of silver provides 25% of silver needs in the society at large greater part of which is gotten from photographic films, papers and x-ray films (Jariwala et al., 2015). Photographic films, papers and x-ray films are most often coated with silver halides such as silver chloride and silver bromide according to Jariwala et al., (2015). After exposing the photographic films to light to capture an image, then the unexposed films containing silver ion remains on the film which later appears as black spots in which the recovery process explores the stripping of those unexposed films containing silver ions to obtain a silver metal(Adani et al., 2005).
Silver is generally obtained from natural sourcesalso as by-products of metallurgical and industrial processes which has been applied in different areas like the electronic, pulp, jewellery and radiographic industries (El-Sayed et al., 2013). Its antimicrobial and anti-inflammatory properties in the medical industries has been very useful in managing burns, roles in antibiotics, surgical and wound dressing (El-Sayed et al., 2013). Gelatin is a protein obtained from the animal collagen that has a large quantity of glycine, proline and 4-hydlroxdyproline residues. In as much as the emulsion layer on the x-ray film contained silver and gelatin, it is then possible to breakdown the gelatin layer using sodium hydroxide to release the needed silver content (Nakiboglu et al., 2001).
Several technologies and methods for silver recovery from used x-ray films such as burning the film, electrolysis metal replacement, bacterial enzymatic methods and chemical precipitationmethod. Except chemical precipitation methods, the other methods are very expensive and time consuming to obtain silver. However, using the chemical precipitation methods does not need much time, not expensive technology, fast and simple to run. It shows that silver recovery using sodium hydroxide as extractant is more advantageous thus, this research work is design to recover silver from x-ray films using sodium hydroxide as extracting agent with much consideration on the concentration of sodium hydroxide, stripping temperature, stripping time and the amount of x-ray films used (Nuri et al., 2003).
1.2 Statement of the Problem
X-ray films in Bori are commonly disposed from the laboratory units of hospitals, medical centers and clinics by the personnel in charge. Daily disposal of these x-ray films to the environment entirely poses a lot of threatsand problems by endangering human health,aquatic lives and agricultural produce due to its soluble nature which can cause organ failure, death of an aquatic organism and stunted growth in plants. Therefore, a good study to assess the level of silver present in x-ray films and the level of environmental pollution through the incessant disposal of x-ray films in Bori metropolis becomes a research problem for the present study. It is therefore important for this current study to access and compare the quantities of the x-ray films used in determining the silver ions concentrations present in the films.
1.3 Significance of the Study
The recovery of silver from x-ray film wastes has benefits economically and environmentally. Therefore, this study will give way for proper environmental evaluation and possibly reuse the silver obtained for a different purpose. This will also reduce the impact of silver related diseases in Bori as well as to improve the health standard of the residents at large.
1.4 Aim and Objectives of the Study
1.4.1 Aim of the Study
The aim of this study is to extract silver metal from hospital x-ray films using sodium hydroxide.
1.4.2 Objectives of the Study
The specific objectives are to;
- Extract silver from the x-ray films.
- Quantify the amount of silver present in the extract.
iii. Compare the amount of silver ions present in the extract by the different concentration of sodium hydroxide.
1.5 Justification of the Study
The recovery of silver from x-ray films waste has a whole lots of benefits amongst which include; saving the environment,reusing the recovered silver for other purposes, reduce silver related diseases in Bori metropolis and to recycle waste x-ray films for commercial purposes.
1.6 Scope of the Study
This research work covered the analysis of silver recovery procedures from hospital x-ray films using sodium hydroxide as extractant and sodium sulphide as a precipitating agent. This study also extended to literally discussing on the health impact of unlawful disposal of x-ray films on the resident and possible solutions.
1.7 Definition of Terms
This research work covered the definitions of some key words in the body of the work, these includes;
- Silver Recovery: This involves the complete removal of silver from x-ray films waste in purity of 99.9% of silver for reuse in other different applications.
- X-ray Film: This is a radiography that consists of an emulsion gelatin which contains radiation sensitive silver halides crystals like silver bromide and silver chloride.
- Photographic Film:This is a strip of transparent plastic film coated with a gelatin emulsion containing microscopically small light sensitive silver halides crystals.
- Metallurgy: This is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds and their mixtures which are called alloys.
- Electrolysis: This is the process by which ionic substances are decomposed into lighter substances when an electric current is passed through them.
- Precipitating Agent: This is a causative substance that affects the formation of suspensions in solution.
- Stripping: This is physical separations that involves the complete removal of coverings from something or a process where one or more components are removed from liquid stream by vapor stream.