# DIY filtering anyone?



## autumnwillow (Feb 5, 2017)

Filtering is one of the most used techniques here but often lack the attention as most leave them overnight but not me, I like to get things done fast. The buchner funnel and GSP's wick system no longer works for me. Its just taking hours or days to filter.

I'm using 125mm buchner funnel with a #1 filter then along with GSP's wick trick.
Filtering the following:
4L gold chloride 250g content takes three to one day depending on silver chloride content.
Gallons of copper chloride with about 1-2kg silver chloride content takes two hours.
Gallons of sulfuric acid with about 1-2kg silver powder content takes hours to a day.
All includes washing.
I also want to filter my waste solution to speed things up as its fumes are stinky.

Has anyone have any good ideas about how to build a large filtering system?
Tabletop buchner funnels a bit too pricey.


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## g_axelsson (Feb 5, 2017)

I have seen posts with filtering setups made by PVC, creating large vacuum filters, but I couldn't find it on a quick look through.

If you really need to speed things up a filter press is a good tool.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=9641&p=105387#p92527

Sorry I couldn't help more.

Göran


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## philddreamer (Feb 5, 2017)

Here's a member's home made pressure filter:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=12143&p=119490&hilit=10+inch+pvc+filter#p119490

Take care!
Phil


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## snoman701 (Feb 5, 2017)

Spread out the area.

HDPE screen that you lay a 6" filter paper on is going to filter a lot faster than a 3" filter. 

Also, if I have a liquid that's hard to filter, I filter in smaller aliquots. The goal is avoidance of filter saturation.


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## goldsilverpro (Feb 5, 2017)

autumnwillow said:


> Filtering is one of the most used techniques here but often lack the attention as most leave them overnight but not me, I like to get things done fast. The buchner funnel and GSP's wick system no longer works for me. Its just taking hours or days to filter.
> 
> I'm using 125mm buchner funnel with a #1 filter then along with GSP's wick trick.
> Filtering the following:
> ...


Filtering has always been the biggest bottleneck in refining. You can't avoid this totally, but there are things you can do to speed things up. Although I have used vacuum filtering all my life, for certain things (like pure gold powder), I prefer gravity filtering for most things, including the 3 items you mentioned in your post. With some things, like large amounts of old AgCl, vacuum filtering tends to pack the solids and this results in very slow filtering. The wick filter is best used for large volumes of difficult to filter sludges - for example, metal hydroxides or emulsion sludges from film. I never used it for the items you mentioned and I think other ways are better for those. 

The gravity filter setup I used consisted of a piece of 3/4" plywood sitting on a bucket. I cut a hole in the plywood so that a large plastic funnel would rest in it about halfway up. In many cases, I had as many as 10-12 of these running at the same time. It's a lot cheaper and easier to set up a lot of gravity filters than it is to set up a lot of vacuum filters. It's hard to make an individual filter go faster but adding more filters will speed things up. 

With gravity filters, it helps to "flute" the filter paper. Fluting effectively increases the surface area of the filter paper 2 or 3 times. Basically, You fold the paper into an accordion shape. To make the fluting perfect takes a lot of time. I found that the folds don't have to be perfect at all. I can flute a filter paper, no matter how large, in a minute or two.
https://encrypted.google.com/search?hl=&q=fluted+filter+paper+done&sourceid=navclient-ff&rlz=1B3MOZA_enUS408US409&ie=UTF-8&lr=all

For aqua regia gold solutions containing some silver, here's how I do it. This goes pretty fast. With the other 2 items in your post, you can do this similarly. However, you can cut down on the amount of dilution if there is no silver. I always like at least a 1 to 1 dilution with most things because it usually speeds up the filtering. An example of where I always dilute 1 to 1 is on silver solutions before cementing with copper.

*(1)* After dissolving, I dilute the solution with 3 times more tap water than then AR volume. This drops out probably 99% of the silver as AgCl. You can use ice to drop the Ag, but it's a pain to do it and it won't drop as much Ag as dilution. After dilution, I add a little sulfuric to drop any lead that might be present. 1st NOTE: AgCl is much more soluble in a strong AR solution than in a weak one. If you didn't dilute before filtering, you would find that, when you rinse the filtered material, it would dilute the already filtered solution. This would cause AgCl to precipitate in the filtered solution and you would be back to square one. 2nd NOTE: You can eliminate (or reduce) the diluting and use something to dissolve the AgCl that is mixed with the gold powder. The old standard is ammonia but, although I have never tried it, I like Lou's method of dissolving it with hot (I think) conc. HCl. 3rd NOTE: Besides dropping most of the silver out, 3X dilution, in my opinion, also makes the gold precipitation almost trouble-free. It also reduces considerably the effects of excess nitric acid. Although I always add the nitric in increments, I sometimes get a bit sloppy and overdo it. Even with too much nitric, when I dilute 3X, I can't remember ever having to eliminate excess nitric before dropping the gold.
*(2)* Allow everything to settle. It's best to wait until the solution is clear but sometimes that takes too much time. Usually, there will be a slight cloudiness.
*(3)* Siphon the settled solution into a clean bucket, Go as far as you can without disturbing the settled solids.
*(4)* Clean 2 buckets. Set a gravity filter on one of the buckets and filter some of the siphoned solution. I prefer a lab paper that is medium fast. After some of the solution has run through, pick up the funnel and examine the solution coming through the tip of the funnel. At first, this filtered solution will usually be cloudy. At some point, the pores in the paper will clog enough so the filtered solution runs clear from the ip of the funnel. Stop adding solution to the funnel. 
*(5)* Pick up the plywood and funnel and transfer it to the second bucket. Re-filter the filtered solution in the 1st bucket and then filter the rest of the siphoned solution in the same paper.
*(6)* When all the siphoned solution has all run through the filter, transfer the solids to the same paper with a squirt bottle.
*(7)* When everything has been filtered, rinse several times. It's faster and more efficient to use several small rinses (just barely cover the solids with water) than to use large rinses (filling the whole funnel with water).
NOTE: You can do the same thing with 1 buchner funnel and 2 filter flasks, but it's more of a pain than with gravity filters.

Another trick:
If you're filtering a large amount of silver chloride from a nitric solution in a vacuum filter, it will pack and take forever. I have found that this will speed up maybe 10 fold by first filtering some AgCl that is freshly made by dissolving some silver in nitric and dropping it with HCl. As soon as the AgCl is made, I filter it. I usually use enough to made about a 1/2 base layer on the paper. Then I filter the other AgCl on top of it. When AgCl sits around, whether wet or dry, it tends to change and can become much slower to filter.

About the only thing I prefer a vacuum filter for is when filtering pure gold powder from an AR solution. After filtering and rinsing, I dry the gold in the filter by placing an incandescent light above the funnel and sucking the heat through the gold. Much less gold will stick to the paper and it's very fast. The downside is that, if the bulb is too close, it can char the paper and produce a huge mess. It's amazing how hot the gold powder can get. I would start with a 60W bulb at least a foot above the funnel.

Like snoman said, a plastic screen will work great in a vacuum filter (as originally posted by 4metals). I've used them quite a bit. However, when all is said and done, I still prefer having several gravity filters. I have also used a plastic screen between the paper and funnel in a gravity filter and it helps somewhat.

For very large quantities, I have used many types of commercial filters. Probably the one I used most is an Alsop filter. In one place, we made 1000's of pounds of nickel carbonate from nickel sulfate and sodium carbonate. It was very similar in constituency as nickel hydroxide - hard to filter. We bought a neat filter which generated a cake and then automatically rinsed it and de-watered it.. The cake was 2-3" thick and came out of the filter on about a 20" conveyor.

FINAL NOTE: Those that are interested in this post might want to re-read it. I added some stuff.


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## aga (Feb 5, 2017)

Thanks for the Wonderful practical filtering advice goldsilverpro !



goldsilverpro said:


> When AgCl sits around, whether wet or dry, it tends to change and can become much slower to filter.



It is odd how some chemicals change over time without actually 'reacting' with anything.

Iron Oxide (rust) is like that - fresh stuff reacts fast, ancient stuff almost not at all.

An explantion once given to me was that the atoms in the crystal matrix pack themselves ever tighter over time.

Edit: swapped 'molecule' for 'crystal matrix'


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## goldsilverpro (Feb 5, 2017)

AgCl, when dry, tends to crystallize. This makes it quite difficult to convert it to silver metal. The NaOH, or whatever, tends to affect the surface of the crystal but is very slow to (or never does) penetrate to the interior. Thus - incomplete conversion. For this reason, there have been articles on the forum, warning people to never let the AgCl dry out.


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## Palladium (Feb 6, 2017)

Google youtube for Bounty Buchner Funnel.


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## rickbb (Feb 6, 2017)

I made one from a 5 gallon bucket with lid, a large plastic kitchen colander, large commercial size coffee filters and a small shop vac. I can filter 3 gallons of AP solution in about 30 minutes.

Looks cobbled together, but it works and was very cheap.


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## autumnwillow (Feb 6, 2017)

Very interesting guys. 

I think i'll try snoman's technique. 
I'll use two wicks on a buchner funnel, first the funnel, a wick, filter paper fit to size of the funnel, a wick again, then a bunch of filter papers overlapping each other that does not necessary have to fit.

GSP, how long does it take for you to gravity filter? I have a bunch of spare buckets to try this one out too.


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## goldsilverpro (Feb 6, 2017)

autumnwillow said:


> Very interesting guys.
> 
> I think i'll try snoman's technique.
> I'll use two wicks on a buchner funnel, first the funnel, a wick, filter paper fit to size of the funnel, a wick again, then a bunch of filter papers overlapping each other that does not necessary have to fit.
> ...


It depends on the type material, how well it's settled, your siphoning expertise, the type paper, and whether or not it's fluted. The siphoned solution from well settled material will filter very rapidly, especially with fluted paper. Also, coffee filters are generally the worst filters you could use. I've used them as much as anyone but, when decent lab paper is available, that's what I use. In the early days, I used high retention slow paper like Whatman 42. Like molasses. I haven't used slow papers for general large volume filtering for 40 years. I discovered that medium or even fairly fast paper works well once it becomes partially clogged. If you use my method and if the material is well settled and well siphoned, the only thing that goes slow is when you finally put the solids along with a small amount of solution in the filter.


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## Topher_osAUrus (Feb 6, 2017)

autumnwillow said:


> ...then a bunch of filter papers overlapping each other that does not necessary have to fit..



That can be troublesome at times, as the top paper (or three) will float freely in the solution.


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## upcyclist (Feb 7, 2017)

I have no idea if what I'm doing is backed by science or not, but I have a tendency to use two fast filters when filtering nitric solutions (with a Buchner/vacuum setup), rather than one slower one, because I think the nitric will dissolve the one paper fairly quickly. That may not matter once it packs with material, though.

But I have also found that using multiple filters seems to make it easier for the resulting damp cake to drop out of the funnel into a drying dish...


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## anachronism (Feb 17, 2017)

I recently had the pleasure of watching pressure filters being used commercially in Australia. I was utterly staggered that they used standard paper instead of filter paper. The volumes and speeds that the liquid was passed through them was staggering. 

Let's just say that "me want one."


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## Topher_osAUrus (Feb 17, 2017)

anachronism said:


> I recently had the pleasure of watching pressure filters being used commercially in Australia. I was utterly staggered that they used standard paper instead of filter paper. The volumes and speeds that the liquid was passed through them was staggering.
> 
> Let's just say that "me want one."



Thats sounds pretty interesting Jon.
Do you happen to have a link, or a youtube video of one that is in operation?

Is this something that would could be constructed or is it too specialized a piece of equipment?
Either way, I'd still like to see it in action!


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## g_axelsson (Feb 17, 2017)

There are a couple of videos linked on this page.
http://goldrefiningwiki.com/mediawiki/index.php/Filter_press

Harold's home built filter press.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=9641&p=105387#p92527

Göran


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## kurita Filter Press (Aug 24, 2017)

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You can google to find their website.


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