# Filter type: Polishing pregnant AR



## Lightspeed (Sep 19, 2017)

Quick question to the experienced members with filtering AR solution.

I have a porcelain Buchner funnel/filter which is fine for my silver cement clean up, I only use gravity filtration before cementing out as the cement is destined for further processing eg shot/cell. From my research though polishing of pregnant AR is a different matter as it is directly related to the purity in the end precipitate, not that silver purity is not important or related to filtration, just that the process for my end product is completely different.

I am looking for advice or some general input from experienced members on filtration apparatus setup for polishing AR-Chloroauric pregnant solution, specifically the pro's and con's of using a porcelain Buchner funnel/filter for AR or using a fritted glass setup like lazersteve in his dvd. The fritted glass type I have absolutely zero experience with.

The porcelain type, regarding filtering a solution for the purposes of polishing pregnant AR before precip stage:

Does the lack of precipitate/weight cause issue with filtration even with vacuum, eg wicking/ seeping behind the filter paper necessitating multiple filtrations process?

Anyone with any recommendation toward a specific type of filter for AR polishing??

Do I need to invest in a glass frit type split cylinder?


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## 4metals (Sep 19, 2017)

Steer clear of frits unless you are working with material you know dissolves completely with no residue. they clog easily and are difficult if not impossible to clean. 

The entire small to medium scale refining industry uses buchner funnels, usually porcelain funnels. The filter media is the key to getting the solution clear or polished as you say. 

Glass fiber filters with a fine retention are the best for AR and as long as they lie completely in the funnel and not up the sides, they seal on the perimeter section with no holes. Too big and they lose the ability to make a seal. 

There are tricks discussed before about making the filter setup filter faster but first thing is the proper medium and the right size.


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## Lightspeed (Sep 19, 2017)

Thanks 4metals,
I will purchase a new porcelain Buchner funnel for Au specific usage.

Regarding the glass papers in commercial usage, is that due to ph of the solution?

I currently use a 90mm paper, with silver cement I have found it necessary to use a double paper, the bottom paper always remains clean underneath contacting the funnel surface, but between the two papers there is a small ring around the seal edge on the paper where a very small amount of silver precipitate manages to find its way in. I have not managed to eradicate this issue regardless of trying various vacuum start up methods with wet papers. I am not concerned as the filtrate is always clarified with zero particulate settling.

Not on topic but related to vacuum filtration, I am using a rotary vane vacuum pump @45litres per minute, with the boiling DW rinse, condensate from the temp of the water builds up in the vacuum line and inevitably enters the pump, which then takes hours to expel from the oil inside the pump. 

Can a simple water trap from a compressor be used to remedy this? 
Rigged inline to suit vacuum not a compressor, I would like to hear on what other forum members are using to avoid the same issue if using a rotary vane pump.

I do not use the flyscreen piece under the filter paper, I have found it unnecessary to this point to aid in filtration speed of silver precipitate, the particulate seems to be of ample size and does not impede the process/flow speed to the point of filter paper breakage under vacuum. This may change regarding a new brand of paper I am going to trial.

http://www.microscience.com.au/wp-content/uploads/.../MicroScience-Catalogue-2013.pdf

EDIT: that link to the pdf seems to be broken, google- microfiltration-microscience.

only due to the fact that they are locally produced and against the Whatman are an economically viable option. The Microscience papers do make an equivalent to the Whatman grade 2 and 5 or very close to the spec. 

Thanks again for the feedback 4metals.


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## nickvc (Sep 20, 2017)

When using a vacuum pump I always set up a trap using an Erlenmeyer flask with a solution of lye in it, you can set it to bubble any gases through the solution protecting your pump from any acidic fumes or any acids, simply use a rubber bung, drill holes through it and use glass tubing as connectors to your vacuum lines, it also pays to service your pump regularly and try to keep it out of acidic fumes or fit another line to draw clean air into your pump, treated correctly pumps can last for many years and will save you time and money.


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