[mehrdadtaheran]

 :)Hi friends
I am a new member
Please help me with this matter.
I want to make a composite of alumina and oxalic acid(or pottasium oxalate), This composite will polish the marble stone with reaction with calcium carbonate and forming calcium oxalate and eroding this compound with alumina. I decided to use MgO+MgCl2 cement to make my composite cheaper. but unfortunately oxalic acid (or pottasium oxalate) react with MgCl2 and the paste wont cure.
how can I prevent the acid from reacting with MgCl2?
I am wondering about a to stage reaction: 1:reacting oxalic acid with Mg(OH)2 and forming magnesium oxalate and drying it. making the composite with magnesium oxalate instead oxalic acid(or pottasium oxalate). this compound will not react with MgCl2, But I am not sure if it react with calcium carbonate to form calcium oxalate.
 

[Hunter2]

Oxalate react with  earth alkali metals  to build precipitates. I think want you want to do will not work.
The solubility  drops from Magnesium to Calcium. Magnesium oxalate L = 0,246 g/l, Calcium oxalate almost insoluble.

[Arkcon]

Well, someone was doing something very similar in this thread here:  http://www.chemicalforums.com/index.php?topic=64616.0  Its a long thread, and kinda all over the place, but still is a beginning of an explanation of your task at hand.

[mehrdadtaheran]

Oxalate react with  earth alkali metals  to build precipitates. I think want you want to do will not work.
The solubility  drops from Magnesium to Calcium. Magnesium oxalate L = 0,246 g/l, Calcium oxalate almost insoluble.

you mean that for formation of calcium oxalate, it is necessary to be soluble?