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GB 8921-2011: Limit standards for 226Ra in phosphate fertilizer and its compound fertilizer
GB 8921-2011
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 13.280
C 57
Replacing GB 8921-1988
Limit standards for 226Ra in phosphate fertilizer
and its compound fertilizer
ISSUED ON. DECEMBER 30, 2011
IMPLEMENTED ON. MAY 01, 2012
Issued by.
Health Ministry of the People’s Republic of China;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1.  Scope ... 4 
2.  Normative references ... 4 
3.  Terms and definitions ... 4 
4.  226Ra limit in phosphate fertilizer and its compound fertilizer ... 5 
5.  Inspection requirements ... 5 
6.  Result judgment ... 5 
Annex A ... 6 
Annex B ... 8 
Foreword 
Chapter 4, Section 5.1, and Chapter 6 in this Standard are compulsory; the rest are
recommendatory.
This Standard was drafted according to the rules given by GB/T 1.1-2009.
This Standard replaces GB 8921-1988 Limit standards for 226Ra in phosphate fertilizer
and its compound fertilizer. Compared with GB 8921-1988, the modifications of this
Standard mainly include.
— The applicable scope is expanded from phosphate fertilizer to phosphate fertilizer
and its compound fertilizer;
— This revision reserves the GB 8921-1988’s limit requirements of 226Ra in
phosphate fertilizer; and deletes the requirements to phosphate ore.
— Provide the methods of sample collection and preparation in the form of Annex;
and add the method of analyzing 226Ra with γ energy spectrum.
This Standard was proposed and shall be centralized by the Ministry of Health of the
People's Republic of China.
This Standard shall be interpreted by the Ministry of Health of the People's Republic of
China.
Drafting organization of this Standard. Health Supervision Institute of Jinlin Health
Department.
Main drafters of this Standard. Yan Chuang, Sun Wuchang, Li Tao, Shi Yan, An Fucai,
Piao Yongde, and Wang Kexin.
The previous version replaced by this Standard is.
- GB 8921-1988.
Limit standards for 226Ra in phosphate fertilizer and its
compound fertilizer
1. Scope 
This Standard stipulates the 226Ra’s limited indicators in phosphate fertilizer and its
compound fertilizer (hereafter abbreviated as phosphate fertilizer), as well as the
corresponding sampling, inspection requirements, and the result judgment.
This Standard applies to the agricultural (including vegetables, fruits and other food crops)
phosphate fertilizer.
2. Normative references 
The articles contained in the following documents have become part of this document
when they are quoted herein. For the dated documents so quoted, all the modifications
(including all corrections) or revisions made thereafter shall be applicable to this
document.
GB 11713 Standard methods of analyzing low specific gamma radioactivity samples
by semiconductor gamma spectrometers
GB 11743 Determination of radionuclides in soil by gamma spectrometry
3. Terms and definitions   
For the purpose of this Standard, the following terms and definitions shall apply.
3.1
Phosphate fertilizer
It is a kind of chemical fertilizer, of which phosphorus is the unique nutrient element.
3.2
Compound phosphate fertilizer
It is a kind of chemical fertilizer containing phosphorus and other nutrient elements (such
as nitrogen and potassium).
4. 226Ra limit in phosphate fertilizer and its compound fertilizer 
226Ra content in phosphate fertilizer and its compound fertilizer shall not be higher than
500 Bq·kg-1.
5. Inspection requirements 
5.1 The quality inspection department of manufacturer shall conduct sample collection
once a year; collect the samples when the production process or raw materials or mix
proportion are changed; and send to the qualified testing agency for inspection.
5.2 The collection and preparation of samples of phosphate fertilizer and its compound
fertilizer shall be carried out according to the method given in Annex A.
5.3 The measurement and arbitration of 226Ra content in phosphate fertilizer and its
compound fertilizer shall be conducted according to emanation scintillation method given
in Annex B.
5.4 The measurement of 226Ra content in phosphate fertilizer and its compound fertilizer
shall be conducted according to γ energy spectrum method given in GB 11713 and GB
11743.
6. Result judgment 
If the 226Ra content in phosphate fertilizer is tested to be less than 500 Bq·kg-1, it is
deemed as qualified. If the 226Ra content in phosphate fertilizer is tested to be more than
500 Bq·kg-1, it shall re-collect the test samples; if the retest result still exceeds 500 Bq·kg-1,
it is deemed as unqualified.
Accurately weigh 1.00g of sample; put it into the nickel crucible; add 2 - 4 g of anhydrous
sodium carbonate and 6g of sodium peroxide; stir evenly; then uniformly cover a layer of
about 3g of sodium peroxide. Put the crucible into 650-700°C muffle furnace; melt it for
7-8 minutes; when the melt is in red fluid, take it out and slightly cool it.
B.4.2 Extraction
Put the outer wall of crucible into cold water for "decladding"; then put it into a 500 ml
beaker; extract it with 200 ml of hot distilled water; after the end of violent reaction, clean
up the crucible with a bit amount of dilute hydrochloric acid; then thoroughly rinse the
crucible and watch glass with distilled water; add 3 ml of 0.02 mol barium nitrate solution;
and heat it to nearly-boiling; then take it down.
B.4.3 Separation
Filter the above solution on the quantitative filter paper; use 0.1 mol sodium carbonate
solution to wash and precipitate for three times; use distilled water to wash one time;
discard the filtrate.
B.4.4 Dissolution and sample sealing
Dissolve the sediment in a 50ml beaker with 3 mol mixed liquor of hydrochloric acid and
small amount of citric acid; transfer the solution into a 100 ml diffuser; use hot distilled
water to wash the filter paper to be without-yellow; control the total amount of solution to
be about 35 ml; exhaust the air with vacuum pump for 5 minutes; then seal it for a week;
and record the sealing time.
B.4.5 Gas pushing
Connect the scintillation chamber that has been vacuumed and of which the background
level has been measured, the drying tube, the diffuser filled with sample solution, the
activated carbon tube, and bubbling tube according to the Figure B.1. Firstly, open the
head of scintillation chamber and diffuser at the beginning of gas pushing; then slowly
open the glass head of active carbon tubes; control the air velocity to be about 120
bubbles/minutes; then speed up the air supply rate; control the air supply time to be within
15 minutes.
B.4.6 Measurement
After gas pushing, leave the scintillation chamber alone for 3 hours; then carry out three
times of measurement under the selected good operating condition, 10 minutes for each
time.
B.4.7 Exhaust
After measurement, immediately use vacuum pump to eliminate radon gas and its
daughter elements, and wash it with nitrogen; make the scintillation chamber recover to
Istandard — Net counting rate of measured 226Ra standard solution, unit. count/min.
B.5.2 Calculation of 226Ra content in test sample
226Ra content cRa (Bq·kg-1) in test sample shall be calculated according to Formula (B.2).
cRa=K·I / m(1-e-λt) ... (B.1)
Where.
cRa — 226Ra content in test sample, unit. Bq·kg-1;
K — Conversion coefficient of scintillation chamber, the 226Ra Bq number of device
responding to 1 count/min, unit. Bq·min/count;
I — Net counting rate of measured test sample, unit. count/min;
m — weight of measured test sample, unit. kg;
λ — Decay constant of radon, unit. every day(d-1);
t — Cumulative time of radon, unit. day (d).
B.6 Precision
The difference between two parallel test results shall not be greater than 20%.