| الملخص | Bench scale experiments were carried out to upgrade low grade Ca-montmorillonite claystone from Wadi Bashiera deposit in the Western Desert. Mineralogically, the dominant gangue mineral is calcite with accessory of quartz and gypsum. The beneficiation process adopted was a dispersion sedimentation method, using sodium hexametaphosphate and tetra sodium pyrophosphate (TSPP). Centrifugal sedimentation was applied for the separation of the gangue, and dewatering of montmorillonite concentrate. Beneficiation operation under the conditions (2 wt % solid concentration, 15 minutes stirring time, 0.6 wt % sodium hexa metaphosphate, and 7minutes mixing of clay slurry and dispersant) effectively removed the majority of the associated calcite and quartz. The montmorillonite concentrate after sodium activation, posse's rheological properties which fit API specification for drilling fluids.
Key: Montmorillonite، upgrading، Beneficiation sedimentation
Introduction
Montmorillonite is belongs to smactite group of clay minerals which has 2:1 type layer structure and possesses high CEC (Grim, 1968 and Bowyer, 2000). Montmorillonite deposits may contain variety of mineral impurities (clay and non- clay), which vary considerably in type and quantity.
Wadi Bashira montmorillonite claystone deposit which located in the Western Desert of Iraq, is of low quality. It contains (on averages) 68% montmorillonite associated with clay and non- clay mineral impurities represents about 32 wt% of the deposit. Calcite, however is the main impurity (Al- Bassam and Saeed, 1989). Sample from this deposit was previously subjected to upgrading on a laboratory scale using dispersion sedimentation process (Al-Ajeel et al., 2008). In the present work beneficiation on a bench scale to assure the feasibility of the process, when processing a larger amounts of material is processed. Furthermore, activation the concentrated clay by sodium for uses in oil well drilling was also investigated.
Experimental work
Sample of low grade montmorillonite claystone from Wadi Bashira deposit was prepared by successive crushing and screening for the experimental work. The chemical and mineralogical compositions are shown in Table 1. It can be seen that the raw claystone contain high CaO amount (14.7 %) which is related to the presence of calcite. Other impurities present are quartz and miner gypsum.
Slurry of 3 kg raw montmorillonite claystone was prepared by high shear mixing with water and sieving on 75 micron sieve (to remove +75 micron particles). Sodium hexameta phosphate (SHMP) and tetra sodium pyrophosphate (TSPP) were used to disperse the clay. The effect of the amount of these materials and solid concentration of the slurry on the impurities separation, particularly calcite (represented by the % CaO) on the purity of the upgraded claystone was studied. The results are presented in Fig.1 and 2.
Discussion and Conclusion
Fig. 1 indicated that, the CaO value of the beneficiated claystone decreases as the amount of the (SHMP) increases to 0.6 wt % and then increases as the (SHMP) increased to 0.8 wt %. The lower CaO value (3.7%) was achieved at 2 wt % solid concentration and 0.6 wt % SHMP. In case of using TSPP(Fig.2), it can noticed that there is no similarity in the way of its effect as that of SHMP(Fig.1), and the lower CaO value (3.7 %) was achieved with 0.8 % TSPP at 2 % solid. According to (Fig.2) this value bore no significant difference than that obtained (3.9 % CaO) with 0.6 wt % TSPP. Therefore, for economical reason stand point, an amount of 0.6% TSPP can be considered optimum. From these results, it can be claimed that (SHMP) is more recommended as a dispersing agent than (TSPP). The chemical composition and CEC of the montmorillonite concentrate produced by this work at the optimum condition (2 wt % solid concentration, 15 min stirring time, 0.6wt % Sodium hexametaphosphate, and 7 minutes stirring of slurry and dispersant) are shows in (Table 2), Compairing these results with that of the starting claystone (Table 1), it can be seen that, the beneficiation process resulted in a high quality montmorillonite clay as the CaO value reduced from 14.7 % CaO to 3.36 % CaO in concentrate and the CEC increased from 60 meq/ 100g to 98 meq /100g. Furthermore, the activated montmorillonite concentrate was found to fulfill API specification for oil well drilling fluids. According to the experimental results it can be concluded that:-
-Dispersion and centrifugal sedimentation process using either sodium hexa met phosphate (SHMP) or tetra sodiumpyrophosphate (TSPP) (preferably the former one) at low slurry concentration are very effective in upgrading the low grade Wadi Bashira montmorillonite claystone.
Reference
Al-Bassam, K.S. and Saeed, L.K., 1989. Mineral investigation of the upper cretaceous Safra montmorillonite claystone deposit, Wadi Bashiera, Western Desert. GEOSURV, int. rep. no. 1922.
Bowyer, P.K., and ledoux, V.M., 2000. Bentonite-more than just dirt.
Grim, R.E., 1968. Clay Mineralogy. MC-Grow Hill Book Company, 2nd edit., 569pp.
Al-Ajeel, A., Abdullah, S., 2008. Beneficiation of Montmorillonite Claystone of Wadi Bashiera (Al-Safra Bed). GEOSURV, int. rep. no. 3120.
Mineralogical Composition
Montmorillonite, Calcite, Quartz, Palygoreskite and minor of gypsum
Chemical Composition
(Wt %) CEC (meq/100gm)
SiO2 Fe2O3 Al2O3 CaO MgO SO3 Na2O K2O Cl L.O.I 60
43.93 4.35 11.16 14.71 3.28 0.30 1.41 0.38 0.95 19.24
Table 1: Mineralogical and chemical composition of the investigated claystone sample
Table 2: Chemical analysis of the beneficiated Montmorillonite
(Wt %)
SiO2
Fe2O3
Al2O3
CaO
MgO
SO3
Na2O
K2O
TiO2
Cl
L.O.I
CEC (meq/ 100gm)
54.92
5.04
16.8
3.36
3.7
0.08
1.33
0.79
0.83
0.957
11.17
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