The REEs are desorbed quantiatively from activated carbon, by completely oxidizing and solubilizing AC by wet digestion (HNO3 and HClO4 treatment ).

Thus the time consuming and tedious method of ignition of charcoal to ashes is avoided, to increase the sample throughput in geochemical exploration studies .

http://www.indianchemsoc.org/jour2013.htm, Abstracts of Journal of Indian Chemical Society Vol.90, November 2013, pp. 1919-2156 , V. V. Hanuman and G. Chakrapani, J. Indian Chem. Soc., Vol. 90, November 2013, pp. 1919-1924.This statement of the authors is absolutely wrong and highly misleading.

In my opinion, dry ashing of the charcoal pellet is the best option and can be completed in 1 hr.

Yes, I fully agree with you. Dry ashing of the charcoal is the best option.

I would be more cautious. If you want to analyse very accurately the elements present if the ashes, acid digestion is the best as all elements will be recovered without losses. Conversely, volatile elements can be lost by calcination, especially alkali, lead, cadmium, etc. If you only have to quantify non-volatile elements, dry ashing is OK, but not for the others. This is the reason why more complex and more difficult methods have been developed.

Alain

Hello there,

Dry ashing is definitely the best and quickest option. However it vey much depends on the temperature of the heat treatments and what analytes you wish to measure. Some elements such as arsenic, antimony and mercury are lost at very high temperatures. There is also a problem of which heating atmosphere you wish to do the ashing in - air or inert gas such as nitrogen. In all cases once the ash is obtained one needs to digest it in mineral acids and put it in solution for elemental determination by ICP-OES, ICP-MS etc. Normal controls such as replicates, operational standards, internal standards and international standards apply for these techniques.

Attaching a copy of such publication on " Simultaneous separation and preconcentration of rare earth elements on activated carbon for its determination by ICP-OES in beneficiation products"..

I have read the above cited paper1, all the cited papers in references and available published literature on the above subject very carefully. Undersigned has been involved in the analysis of geological materials and hydro-geochemical reconnaissance surveys attached with mobile geochemical laboratories in different parts of India for exploration activities of Atomic Minerals Directorate for Exploration and Research. Undersigned is serving as an author and reviewer of Journal of Indian Chemical Society.

This manuscript1 is lacking in any originality, innovation or novelty over the earlier published paper cited as reference no.16 in the manuscript titled “Determination of Rare earth elements in different geological matrices by ICP-AES after solid phase micro extraction on activated charcoal” by D.S.R. Murty, P.L. Mohanta and R. Radhamani, published2 in the journal, Atomic Spectroscopy, 23(2), pp. 65-74, 2002.

 I would like to reproduce from this publication2 abstract section, page no.65 quote  “The  novelty of the method lies in the fact that REEs are adsorbed on activated charcoal as their fluoride complexes….The present method has very wide dynamic range of applicability for a variety of geological samples”unquote. Optimum parameters: 0.5 g of AC, 4 hrs of contact time with occasional stirring, and 5% HF concentration. Desorption studies: page 69, authors recommended-dry ashing of the charcoal pellet after adsorption was carried out by ashing in a furnace at 700 0C for 1 hr, then nitration, dissolving in dilute nitric acid and subsequent determination of REEs by ICP-AES.

In spite of the fact stated very clearly in the publication2 quote “The present method has very wide dynamic range of applicability for a variety of geological samples” unquote. The author, Chakrapani has published a number of papers with the same reagent system, AC as peconcentrator/separator for REEs without any significant improvements over publication2 cited as reference no.16.

Author, Chakrapani etal. published a paper3 titled “ A single stage simultaneous separation and preconcentation of rare earth elements on  activated carbon for its determination by ICP-OES after wet ashing –application to soil samples, published in EARFAM, vol,17, 2007, pp.53-61. The unique feature of the procedure is the same using the reagent system-Activated carbon. The same feature of the method has been described in the publication by Chakrapani4 on page 449, Section 3 vide his publication in Journal of Applied Geochemistry, Vol.,14,no.4 (2012),pp.447-452 and also in his publication titled5  “Determination of rare earth elements in uraninite samples by ICP-OES after solid phase extraction on activated carbon”by P.L.Mahanta, , G. Chakrapani and R. Radhamani,  published in Atomic Spectroscopy, vol.,31,(1),2010, pp.21-26. Both these publications of the senior corresponding author, Chakrapani have neither been cited or nor there is any discussion in the references related with Soild phase extraction on AC for REEs determination in the above cited JICS paper1 by the authors.

Moreover, in the publication by Chakrapani4 in Journal of Applied Geochemistry, Vol.,14, no.4 (2012),pp.447-452,  the main reference on AC by Murty, etal2., Atomic Spectroscopy (2002) ismissing.The authors have suppressed the already reported and published information.

 As stated in the manuscript1, page 1919, quote “The most common physical method for mineral separation is the gravity separation using heavy liquid like bromoform, which is generally used to separate ferromagnesian minerals from quartz and feldspar. Thus, bromoform separated heavier fractions are normally free from quartz and other silicate minerals  and contains refractory mineral phases” .The information on bromoheavies as beneficiation product is same as reported by Chakrapani cited as reference no.20 in the manuscript (without including any title of the paper) and the same has already published vide his publication6 titled “A RAPID SAMPLE DECOMPOSITION PROCEDURE FOR BROMO-HEAVIES CONTAINING FERRUGINOUS MATERIAL: DETERMINATION OF REEs AND  THORIUM BY ICP-AES” by C. R. Khorge, G. Chakrapani and P. Murugesan, Exploration and Research for Atomic Minerals, Vol. 23, 2013, pp. 1-6 . They have applied on samples containing very high concentration of REEs. In the present manuscript, authors have applied to beneficiation product, the  bromoheavies containing low concentration of REEs. This statement of the authors is highly contradictory and misleading.

There is a contradiction on the optimal parameters such as amount of AC and contact time in different publications. For the same reagent system, amount of AC differed from 0.2 g to 1.0 g and contact time from 1 hr1, 4 hr2 and overnight7.As on date, the basic informations on adsorption capacity of AC, thermodynamic parameters  and modeling are missing for such reagent system. The adsorption capacity is an important factor, because it determines how much sorbent is required to quantitatively concentrate the analytes from a given solution. From the available literature8, there is a decrease in adsorption of uranium on AC in the presence of fluoride, nitrate, thiosulphate and oxalate ions can be attributed to weak adsorption of the anionic complexes. Qadeer etal9. published their studies on surface characterization and thermodynamics of adsorption of Sr2+, Ce3+, Sm3+, Gd3+,Th4+,UO22+ on activated charcoal from aqueous solution. In view of the solubility products values of REEs fluorides10 and the conditions used by the authors (3-4 M HF medium) for adsorption of REEs on AC needs further investigations on the role of AC. There is no characterization of AC and REEs sorbed-AC by the authors for their claim. In the cited manuscript1, authors have recommended wet–ashing, quote “The REEs are desorbed quantitatively from activated carbon, by completely oxidising and solubilizing AC  by wet digestion(HNO3 and HClO4 treatment). Thus the time consuming and tedious method of ignition of charcoal to ashes is avoided, to increase the sample throughput in geochemical  exploration studies” unquote. This statement of the authors is absolutely wrong and highly misleading.

Murty etal.2 and Kumar etal.7 have recommended dry ashing of the charcoal pellet in a furnace. In my opinion also, dry ashing of the charcoal pellet is the best option and can be completed in 1 hr. As far as possible, toxic acids fuming should be avoided and is a health hazard. Perchloric acid (HClO4) is an extremely reactive liquid. It is clearly stated in ASTM document14, Designation: C 25-06, Section: Procedure: Warning, page no. 6. quote “When using HClO4, there are precautions to be followed which, if unheeded, may lead to serious explosions. Contact of the hot concentrated acid with organic matter (AC in this case)must be absolutely avoided. Any organic matter in the sample must first be destroyed by the addition of nitric acid (HNO3) to the sample prior to fuming with HClO4”unquote.If proper care is not taken, wet-ashing treatment of charcoal pellet with HNO3 and HClO4 may result in a blast.

Activated carbon (Merck make, Germany) is not a low cost material. Oxalate precipitation method is a well established method for the separation of REEs.  Recovery /separation/preconcentration of rare earth metals through biosorption using low cost biomaterials11 or modified AC12,13 will continue to remain a greatest challenge.

I request that the authors of the subject article kindly further document the reliability of their findings in view of the concerns expressed herein.

References:

1. V.V. Hanuman and G. Chakrapani, J. Indian Chem. Soc.,2013, 90, 1919.

2. D.S.R. Murty, P.L. Mohanta and R. Radhamani, Atomic Spectroscopy, 2002, 23, 65.

3. G. Chakrapani, P. L. Mahanta,V. V. Hanuman and P. K. Srivastava, Exploration and Research for 

    Atomic Minerals, 2007, 17, 53.

4.G. Chakrapani,  Journal of Applied Geochemistry, 2012,14, 447.

5. P.L.Mahanta, G.Chakrapani and R. Radhamani, Atomic Spectroscopy, 2010, 31,21.

6.C. R. Khorge, G. Chakrapani and P. Murugesan,Exploration and Research for Atomic Minerals,  

    2013, 23, 1 .

7. Adarsh Kumar,Beena Sunilkumar,R.Lalithambal and G.S.Chowdary, Exploration and Research for

    Atomic Minerals, 2007, 17,70

8. www.google.com: [PDF] adsorption of heavy metals on activated charcoal

       prr.hec.gov.pk/Chapters/3053H-4.pdf‎  and reference cited therein.

9.Riaz Qadeer, Javed Hanif, M. Saleem and M.afzal,colloid and Polymer Science, 1993, 271,  83  and       

     reference cited therein.

10.Hisako Itoh, Hiromitsu Hachiya, Masashi Tsuchiya,Yasuo Suzukiand Yasukazu Asano, Bull. Chem.   

     Soc.Jpn.,1984,57,1689.

11.Nilanjana Das and Devlina Das,Journal of Rare Earths, 2013, 31,  933.

12.Marwani, H.M. et al., Study of isotherm and kinetic models of lanthanum adsorption on activated    

      carbon loaded with recently synthesized Schiff’s base. Arabian Journal of Chemistry (2013),  

      http://dx.doi.org/10.1016/j.arabjc.2013.01.008.

13.Pei Liang, Yan Liu and Li Guo, Spectrochimica Acta Part B, 2005, 60,125.

14.http://adsl-99-68-174-150.dsl.pltn13.sbcglobal.net/ASTM/PDF/C25.pdf

     [PDF] Standard Test Methods for Chemical Analysis of Limestone, Quicklime, and hydrated Lime.,   

     P.6 , Section, 9.3.