Asbestos, filter aids

Materials suitable as filter aids include diatomaceous earth, expanded perilitic rock, asbestos, ceUulose, nonactivated carbon, ashes, ground chalk, or mixtures of those materials. The amount of body feed is subject to optimisa tion, and the criterion for the optimisa tion depends on the purpose of the filtration. Maximum yield of filtrate per unit mass of filter aid is probably most common but longest cycle, fastest flow, or maximum utilisation of cake space are other criteria that requite a different rate of body feed addition. The tests to be carried out for such optimisation normally use laboratory or pilot-scale filters, and must include variation of the filtration parameters such as pressure or cake thickness in the optimisation. 

The use of asbestos has been greatly diminished because of its identification with health hazards. There have been proposed replacement materials such as the Zeta Plus filter media from the AMF Cuno Division, consisting of a composite of cellulose and inorganic filter aids that have a positive charge and provide an electrokinetic attraction to hold colloids (usually negatively charged). These media therefore provide both mechanical straining and electrokinetic adsorption. 

Commonly used filter aids include diatomaceous earth, perlite, asbestos, cellulose, agriculture fibers, etc. 

Other materials used as filter aids include asbestos, cellulose, rice hull ash, paper fibers, etc. 

Various substances are used albumen, white of egg, fish glue, gelatin, and skimmed milk, or the modern filter aids such as talc, asbestos, kieselguhr, etc. 

Asbestos is a fibrous mineral with conqilex surface properties which make it particularly successfiil in many applications such as the removal of protein hazes fi om beverages. It was often used in mixtures with other filter aids made to form eets, but contains soluble iuqturities of Fe, Mg and Ca. It is rarely used now because of health hazard problems. 

Materials suitable as filter aids include diatomaceous earth, expanded perilitic rock, asbestos, cellulose, non-activated carbon, ashes, ground chalk or mixtures of those materials. Whilst mineral filter aids have been well established in industry for many decades, those based on organic, selfreplenishing raw or even waste materials such as cellulose, wood fibres or plant fibres have been increasing in use. The best situation is when a cheap or reject material can be found elsewhere in the process and is suitable for using as a filter aid, at little or no extra cost. 

The clarification by filtering involves pads of asbestos, cellulose, infusorial earth, and filter aids such as Hyflo Super Cel and Filter Cel. The fil-... 

An apparatus for the filtration of small to moderate quantities of crystals incorporates the so-called Willstatter filtration nail. The latter consists of a thin glass rod flattened at one end. It is readily constructed by heating the end of a short glass rod in the blowpipe flame and pressing vertically upon an asbestos board. The nail is fitted into small glass funnel it is covered by a circle of a filter paper cut with the aid of a cork borer of appropriate size. A filtration nail r r and funnel, capable of handling up to 1 g. of solid is depicted... 

Shower and bath water should be with mixed hot and cold water faucets. Water that has been used to dean jjersonnel or equipment should either be filtered or be collected and discarded as asbestos waste. Soap and shampoo should be provided to aid in removing dust from the workers skin and hair. 

Before describing woven filter media further, it should be noted that there are many filter media available which cannot be detailed in this chapter. The following are some not previously mentioned and they are presented here only in name in order to indicate the vast variety available. Filter sheets are available, formed from diatomaceous earth rather than asbestos. Loose fibre filter media, made from asbestos, cellulose and glass wool, are other types of material available. There are a wide variety of loose particles available as filter media, including precoats, sand or body aids. Body aids are additives to the liquid to be filtered. Lastly, perforated sheets in both synthetic materials and metals are used but have restrictions because hole sizes are generally no smaller than 50 pm. They are commonly used as support or back-up for finer media, or alone as strainers or roughing filters. 

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