الفهرس 
Geology of Phosphate RocksOnly 14 pages are availabe for public view
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Abstract
The utilization of phosphogypsum (PG) as a raw material for
the production of valuable products is interesting. In this
contribution, Rare earth elements (REEs) leaching from dihydrate
phosphogypsum using sulfuric acid was investigated using Onefactor-
at-a-time (OFAT) methodology and Design of Experiment
(DoE) methodology. Based on the OFAT methodology, the influence
of various factors affecting the leaching process such as; reaction
time, sulfuric acid concentration, liquid to solid ratio, leaching
temperature, and stirring speed have been examined terms of high
REEs leaching efficiency and low impurities.
In regards to DoE methodology, the multivariate 23 full
factorial design is used to study the effect of sulfuric acid
concentration, liquid/ solid ratio, leaching time on the REEs leaching
process. The normal first order model (fitted model) between
significant factors and the response was developed by the Design
Expert 11.0 software. The obtained results clarify that REEs leaching
efficiency was 72.3% under the following optimal conditions; 4 %
sulfuric acid concentration, liquid/ solid ratio, ml/ g, 5/1, and reaction
time of 3 hrs.
Dihydrate phosphogypsum, treated with sulfuric acid, has
been converted into calcium carbonate and sodium sulfate using
sodium carbonate. Phosphogypsum conversion process has been
investigated using One-factor-at-a-time (OFAT) procedure and
Design of Experiment (DoE) procedure. Regards to the OFAT
procedure, the effect of different factors such as; stirring time,
sodium carbonate concentration, liquid to solid ratio, reaction temperature, and stirring speed on the conversion process using
sodium carbonate have been investigated.
The full factorial design has been performed to optimize the
conversion of phosphogypsum to carbonate using sodium carbonate.
Four factors were taken into consideration in the experimental
planning: time, solid/ liquid ratio, sodium carbonate concentration,
and temperature. The analysis of variance (ANOVA) has been used
to determine the main effects and interactions between the studied
factors. The optimum conditions have been determined as, sodium
carbonate concentration of 30 %, reaction time of 10 min and solid/
liquid ratio, g/ ml of 1:2. Under these optimum conditions, the
phosphogypsum conversion to carbonate efficiency performance is
95.2 %. The characterization of the produced calcium carbonate has
been achieved using XRF, XRD and FT-IR.
The environmental radiation impact as well as radiation
hazard indices factors (exposure rate and absorbed dose rate,
effective dose rate, the radium equivalent activity (Raeq), external
hazard, internal hazard and (level index) I-gamma) have been
measured and calculated in phosphogypsum working sample,
phosphogypsum leached with sulfuric acid, produced calcium
carbonate, and sodium sulfate. The obtained results clear that, the
produced calcium carbonate, and sodium sulfate have normal level of
natural background where these values are within the world
permissible limits. This means that the produced sodium carbonate
and sodium sulfate are acceptable for use in industrial applications.
Keywords: phosphogypsum, Rare earths, calcium carbonate, full
factorial design, optimization.