Experimental Study On Removal Of Impurities By Ground Calcium Carbonate Powder

The ground calcium carbonate?GCC?itself should be a white powder.However,since GCC powder often contains other metal elements,it exhibits colorful such as light red,grayish black,etc.which affects the whiteness,thereby affecting the performance of the mineral material.In order to increase the whiteness,two processes of sodium bicarbonate-sodium bisulfite-sodium borohydride-sodium citrate?BCSS?and sulfuric acid-sodium dithionite-sodium citrate?DCS?were proposed in this paper.In the experiment,the mineralogical characteristics and blackening causes of GCC powder in a mining company of Anhui were studied by analysis of phase,chemical composition and micro structure.X-ray diffraction?XRD?analysis shows that the GCC mineral consistes of two phases,calcite and dolomite.Chemical composition shows that the blackening elements of the GCC powder samples are Fe,Mn,etc.and the content of calcium carbonate reaches 94%or more.BCSS used the sodium dithionite?sodium bisulfite and sodium borohydride formation?to reduce Fe³⁺to Fe²⁺by adjusting the pH,then Fe²⁺was complexed and other non-ferrous metals Mn.were shielded by sodium citrate.It is found that the BCSS method can increase about 10.00%of the whiteness value of sample 1,the recovery is to be approximately 70.00%,the whiteness value of sample 2 is only increased by 5.00%,and the recovery is less than 50.00%by single factor experiment.At the same time,the whitening mechanism of the BCSS method was discussed,mainly achieving the purpose of whitening by reducing and masking black elements.In order to obtain a more effective whitening method,combined with Aguilera and Jackson's sodium dithionite-sodium citrate-sodium bicarbonate?DCB?method,the sulfuric acid-sodium dithionite-sodium citrate?DCS?method was proposed.It is found that the DCS method of single factor can increase the whiteness value up to90.00%for the sample 1,the recovery is up to 95.00%,the whiteness value of the sample 2 can reach 95.60%and the recovery is about 80.00%.It is found that the DCS method is very effective for the treatment of sample No.2 and both the whiteness value and the recovery are satisfactory.To further optimize the process,sample 2 was taken as an example,the orthogonal study was carried out by DCS method.It is found that amounts of sulfuric acid have the greatest influence on whiteness,and the best process was explored.At the same time,the whitening mechanism of DCS method was studied.For method DCS,one reason is colorful metals are reduced or shield and the other reason is that calcium sulphate is wrapped outside the granules for whitening purposes.The whiteness is improved by the BCSS and DCS methods,satisfying national standards and market requirements,which can be applied to industries such as paints,rubber,and ceilings and so on.The value of ground calcium carbonate is improved.by economic evaluation,and the DCS method provids a new way for effective whitening of ground calcium carbonate.