1.3.1 樣片的制備
將樣品粒度研磨至不大于74μm的分析試樣，稱(chēng)取分析試樣約10g，加入硼酸墊底，于壓片機(jī)上以500MPa壓力條件下壓制30s，壓制成粉末樣片。用洗耳球吹去表面可能存在的顆粒物質(zhì)。制備樣片厚度應(yīng)不少于3mm。樣片表面需平整，無(wú)裂紋、無(wú)粉末脫落等缺陷。
1.3.2 試樣分析
將制備的粉末壓片置于單波長(zhǎng)激發(fā)能量色散X射線(xiàn)熒光光譜儀中獲取熒光強(qiáng)度信號(hào)，采用無(wú)標(biāo)樣全譜擬合-基本參數(shù)法進(jìn)行無(wú)標(biāo)定量分析，計(jì)算得出分析試樣中元素含量。分析試樣進(jìn)行兩次平行測(cè)定取其平均值。
2.結(jié)果與討論
2.1 無(wú)標(biāo)樣全譜擬合算法
基本參數(shù)法分為兩類(lèi)，一是通過(guò)對(duì)已知元素和含量的標(biāo)準(zhǔn)物質(zhì)，輸入標(biāo)準(zhǔn)物質(zhì)的元素和含量經(jīng)過(guò)一系列計(jì)算擬合，確定基本參數(shù)算法；二是對(duì)未知樣品定量分析。采用最小二乘擬合算法對(duì)未知樣品實(shí)測(cè)譜擬合全譜[9]。最小二乘法是從誤差擬合的角度對(duì)回歸模型進(jìn)行參數(shù)估計(jì)。將樣品實(shí)際測(cè)量譜線(xiàn)分解為樣品中各個(gè)單元素在相同樣品基體情況下，樣品中各個(gè)單元素相應(yīng)含量下的理論譜線(xiàn)的疊加。因?qū)嶋H測(cè)量譜線(xiàn)測(cè)量結(jié)束后為固定值，如果假定元素初始含量，用假定含量解出該含量的理論譜線(xiàn)，用測(cè)量譜線(xiàn)對(duì)單元素理論譜線(xiàn)進(jìn)行全譜匹配，匹配結(jié)果為一個(gè)新的含量，不斷重復(fù)全譜匹配過(guò)程，直到元素含量收斂為樣品中元素的實(shí)際含量。本文選擇基于基本參數(shù)法（FP）的全譜擬合無(wú)標(biāo)樣定量算法進(jìn)行分析。
含鐵物料元素組成復(fù)雜，其基體元素成分變化會(huì)直接影響待測(cè)元素特征X射線(xiàn)強(qiáng)度的測(cè)量。低鐵含量樣品（為鐵含量15%以下的含鎳物料）鉻元素檢測(cè)情況表明，對(duì)于與含鐵物料基體（一般鐵含量在40%以上）相差較大的樣品不宜直接利用含鐵物料的檢測(cè)條件進(jìn)行檢測(cè)，說(shuō)明過(guò)大的基體差異會(huì)導(dǎo)致結(jié)果的明顯偏差。利用無(wú)標(biāo)樣全譜擬合算法建立相應(yīng)基體樣品的結(jié)果校正曲線(xiàn)，不改變檢測(cè)條件，可以消除明顯的基體差異導(dǎo)致的結(jié)果偏差，保障檢測(cè)結(jié)果的準(zhǔn)確。選取含有不同含量的各有害元素的含鐵物料，利用基于基本參數(shù)法的無(wú)標(biāo)樣全譜擬合算法進(jìn)行分析，其檢測(cè)結(jié)果與真值的擬合情況見(jiàn)表2。由表2可知，其R2均不小于0.9990。
表2 各元素基本參數(shù)法直接測(cè)定結(jié)果與真值的擬合情況
Tab.2 Fitting of Direct Measurement Results of Basic Parameters of Each Element with True Values
| Element |
Number of samples |
Content range |
R2 |
| Cd |
11 |
0.00082-0.112 |
0.9991 |
| As |
15 |
0.0024-0.668 |
0.9990 |
| Pb |
12 |
0.0073-0.795 |
0.9993 |
| Hg |
4 |
0.0014-0.0089 |
0.9991 |
| Cr（High iron content samples） |
10 |
0.015-1.84 |
0.9999 |
| Cr（Low iron content samples） |
7 |
0.060-0.92 |
0.9991 |
2.2 背景及譜線(xiàn)權(quán)重優(yōu)化
含鐵物料檢測(cè)中，背景來(lái)源主要包括入射X射線(xiàn)的康普頓散射和瑞利散射、探測(cè)器的康普頓散射逃逸效應(yīng)、探測(cè)器的不完全電荷收集效應(yīng)、光電子和俄歇電子逃逸效應(yīng)等。因此，在采用基本參數(shù)法計(jì)算過(guò)程中需要通過(guò)扣背景來(lái)消除或降低背景對(duì)元素峰擬合的影響，但扣背景不足或過(guò)多均會(huì)影響元素檢測(cè)結(jié)果的準(zhǔn)確性。對(duì)樣品號(hào)為Fe-1的含鐵物料譜圖進(jìn)行背景優(yōu)化，針對(duì)含鐵物料的復(fù)雜基體復(fù)雜背景問(wèn)題，為能夠準(zhǔn)確提取微量元素信號(hào)，建立了分段式多參數(shù)背景補(bǔ)償Snip算法。如圖1為Fe-1含鐵物料背景優(yōu)化譜圖。圖中下曲線(xiàn)為掃描Fe-1含鐵物料原始譜圖，上曲線(xiàn)為優(yōu)化后譜圖。經(jīng)優(yōu)化后的譜圖，可提取出低譜峰信號(hào)強(qiáng)度。
圖1 Fe-1樣品背景優(yōu)化譜圖
Fig.1 Optimization spectrum of Fe-1 sample background
2.3 譜線(xiàn)選擇及重疊干擾校正
選擇待測(cè)元素特征譜線(xiàn)時(shí)應(yīng)避免基體中共存元素的譜線(xiàn)干擾、和峰干擾、靶材的特征譜線(xiàn)及其康普頓譜逃逸峰干擾。光譜干擾可通過(guò)選擇適當(dāng)?shù)姆治鼍€(xiàn)和采用干擾校正系數(shù)來(lái)解決。表3中給出了含鐵物料中砷、鉛、汞、鉻、鎘元素檢測(cè)推薦譜線(xiàn)和干擾修正情況。
表3 含鐵物料中微量元素的推薦分析線(xiàn)及干擾情況
Tab.3 Recommended Analysis Lines and Interference Conditions for Trace Elements in Ferrous Materials
| Element |
Recommended spectral lines |
Participate in basic correction elements |
Spectral overlapping interference element lines and typical interference situations |
Interference correction method |
| As |
Kα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The Lα -line of Pb element overlaps with the Kα -line of As element |
Using theLβ -line of Pb element to calculate the content of Pb element, and then re analyzing the Kα -line of As element in overlapping peaks |
| Pb |
Lβ -line |
Fe、 Ca、Si、Al、Mn、K、O |
The double peak of the Kα -line of Fe element overlaps with the Lβ -line of Pb element |
Algorithm of using full spectrum fitting matrix parameters method |
| Hg |
Lα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The overlapping peaks have no interference, but the Lα -line of Hg element is easily affected by the Kα -line and Kβ -line of Zn element, resulting in background interference |
The content of Zn element greater than 1% affects the determination of low content Hg element |
| Cr |
Kα -line or Kβ -line |
Fe、 Ca、Si、Al、Mn、K、O |
The Kα -line of Cr element overlaps with the escape peak of Fe element's Kβ -line and the Kβ -line of V element, while the Kβ -line of Cr element overlaps with the Kβ -line of Mn element |
By calculating the content of Fe, V, and Mn elements, Cr can be further resolved in overlapping peaks |
| Cd |
Kα -line |
Fe、 Ca、Si、Al、Mn、K、O |
The position where the Lβ1 - line of Pb element accumulates and doubles, and the position where the Lα -line of Pb element accumulates and doubles, will have a combined peak |
Deducting the effect of peak concentration by calculating the Pb element content |
2.4 方法檢測(cè)下限及檢出限
選擇SiO2作為空白樣，利用單波長(zhǎng)激發(fā)能量色散X射線(xiàn)熒光光譜法對(duì)其重復(fù)測(cè)定11次，以3.14倍測(cè)定值的標(biāo)準(zhǔn)偏差（s）計(jì)算檢出限（3.14s）[10]。方法的檢測(cè)下限可定義為在特定基體某一可信度內(nèi)對(duì)分析物能進(jìn)行可靠確認(rèn)和定量的最低濃度值，通常取3倍檢出限，結(jié)果保留兩位有效數(shù)字，見(jiàn)表4。
表4 方法檢測(cè)下限及檢出限
Tab.4 Method detection lower limit and detection limit
| Sample number |
Determination of elements |
| Hg |
As |
Pb |
Cd |
Cr |
| 1 |
0.00041 |
0.0016 |
-0.0012 |
-0.00015 |
-0.013 |
| 2 |
0.00037 |
0.0015 |
-0.00090 |
-0.00024 |
-0.013 |
| 3 |
0.00013 |
0.0016 |
-0.0010 |
-0.00024 |
-0.014 |
| 4 |
0.00026 |
0.0015 |
-0.0011 |
-0.00014 |
-0.013 |
| 5 |
0.00032 |
0.0015 |
-0.0013 |
-0.00023 |
-0.014 |
| 6 |
0.00015 |
0.0016 |
-0.00098 |
-0.00039 |
-0.013 |
| 7 |
0.00018 |
0.0014 |
-0.0010 |
-0.00023 |
-0.013 |
| 8 |
0.00015 |
0.0013 |
-0.0010 |
-0.00068 |
-0.013 |
| 9 |
0.00014 |
0.0013 |
-0.00093 |
-0.00021 |
-0.013 |
| 10 |
0.00039 |
0.0016 |
-0.0010 |
-0.00049 |
-0.013 |
| 11 |
0.00036 |
0.0013 |
-0.0010 |
-0.00021 |
-0.012 |
| S |
0.00011 |
0.00011 |
0.00012 |
0.00017 |
0.00035 |
| Detection limit |
0.00035 |
0.00036 |
0.00037 |
0.00052 |
0.0011 |
| Method detection lower limit |
0.0011 |
0.0011 |
0.0011 |
0.0016 |
0.0033 |
2.5 方法精密度
選取含有有害元素的含鐵物料樣片，進(jìn)行精密度試驗(yàn)。分析結(jié)果見(jiàn)表5。由表5可知，各元素RSD在3.19%~9.00%范圍內(nèi)，RSD均不大于10%，精密度良好。
表5 精密度試
Tab.5 Precision test（n=7） /%
| Sample |
As |
Pb |
Cd |
Cr |
Hg |
| average value |
RSD |
average value |
RSD |
average value |
RSD |
average value |
RSD |
average value |
RSD |
| Fe-1 |
0.048 |
4.9 |
0.76 |
4.8 |
0.00092 |
8.7 |
0.056 |
4.8 |
/ |
/ |
| Fe-2 |
0.0042 |
7.3 |
0.10 |
4.2 |
0.0038 |
7.0 |
0.018 |
3.5 |
|
|
| Hg-3 |
0.022 |
4.0 |
0.21 |
3.2 |
/ |
/ |
0.032 |
4.7 |
0.0037 |
9.0 |
| Hg-4 |
0.0085 |
3.4 |
0.18 |
4.9 |
/ |
/ |
0.0098 |
5.6 |
0.0083 |
4.5 |
2.6 方法正確度
選取各元素不同水平含鐵物料樣品，按本試驗(yàn)方法進(jìn)行測(cè)定，并與ICP-MS法、直接測(cè)汞儀法進(jìn)行結(jié)果比對(duì)，檢測(cè)結(jié)果見(jiàn)表6~10。由檢測(cè)結(jié)果可知，砷元素測(cè)定中Fe-2、GSB03-2854-2012及S-4含鐵物料，鉛元素測(cè)定中YSBC28786-2015含鐵物料檢測(cè)結(jié)果與其他方法或標(biāo)示值偏差較大，主要原因?yàn)榻咏浞椒z測(cè)下限。經(jīng)正確度驗(yàn)證，該方法滿(mǎn)足分析要求，可開(kāi)展快速分析檢測(cè)。
表6 砷元素檢測(cè)比對(duì)結(jié)果
Tab.6 Comparison Results of Arsenic Element Detection /%
| Samples |
This method |
ICP-MS measured value |
| Fe-1 |
0.048 |
0.056 |
| Fe-2 |
0.0042 |
0.0024 |
| YSBC14722-98 |
0.11 |
0.10 |
| YSBC28786-2015 |
0.0096 |
0.0095 |
| GSB03-2854-2012 |
0.0064 |
0.0044 |
| GSB03-2855-2012 |
0.22 |
0.22 |
| GSB03-2856-2012 |
0.047 |
0.051 |
| YSBC28785-2015 |
0.013 |
0.011 |
| GSB03-1805-2005 |
0.096 |
0.11 |
| S-4 |
0.0019 |
0.0008 |
| S-1 |
0.094 |
0.097 |
| S-2 |
0.014 |
0.010 |
| S-3 |
0.093 |
0.072 |
| GSB03-2857-2012 |
0.33 |
0.29 |
| Fe-3 |
0.64 |
0.67 |
表7 鉛元素檢測(cè)比對(duì)結(jié)果
Tab.7 Comparison Results of Lead Element Detection /%
| Samples |
This method |
ICP-MS measured value |
| Fe-2 |
0.10 |
0.11 |
| Fe-1 |
0.73 |
0.79 |
| YSBC14722-98 |
0.099 |
0.120 |
| YSBC28786-2015 |
0.0047 |
0.0073 |
| GSB03-2854-2012 |
0.027 |
0.035 |
| GSB03-2855-2012 |
0.16 |
0.18 |
| GSB03-2856-2012 |
0.031 |
0.034 |
| YSBC28785-2015 |
0.012 |
0.020 |
| GSB03-1805-2005 |
0.085 |
0.11 |
| S-1 |
0.44 |
0.47 |
| S-3 |
0.18 |
0.20 |
| GSB03-2857-2012 |
0.18 |
0.19 |
表8 汞元素檢測(cè)比對(duì)結(jié)果
Tab.8 Comparison Results of Mercury Element Detection /%
| Samples |
This method |
Direct mercury meter method |
| Hg-1 |
0.0012 |
0.0014 |
| Hg-2 |
0.0025 |
0.0030 |
| Hg-3 |
0.0039 |
0.0045 |
| Hg-4 |
0.0081 |
0.0089 |
表9 鉻元素檢測(cè)比對(duì)結(jié)果
Tab.9 Comparison Results of Chromium Element Detection /%
| High speed iron containing materials |
Low iron element iron containing materials |
| Samples |
This method |
ICP-MS measured value |
Samples |
This method |
ICP-MS measured value |
| ISO306 |
0.015 |
0.017 |
GBW07146 |
0.13 |
0.12 |
| ISO316 |
0.069 |
0.080 |
GBW07147 |
0.13 |
0.13 |
| ISO315 |
0.031 |
0.036 |
GBW07148 |
0.073 |
0.060 |
| ISO327 |
0.014 |
0.015 |
ZBK413 |
0.80 |
0.76 |
| ZBK459 |
0.055 |
0.047 |
ZBK414 |
0.93 |
0.90 |
| ZBK460 |
0.037 |
0.037 |
ZBK415 |
0.82 |
0.83 |
| ZBK461 |
0.033 |
0.027 |
ZBK416 |
0.76 |
0.76 |
| ZBK418 |
1.31 |
1.38 |
ZBK417 |
0.36 |
0.37 |
| ZBK412 |
1.75 |
1.84 |
/ |
/ |
/ |
| GBW07149 |
0.055 |
0.046 |
/ |
/ |
/ |
表10 鎘元素檢測(cè)比對(duì)結(jié)果
Tab.10 Comparison Results of Cadmium Element Detection /%
| Sample |
This method |
ICP-MS measured value |
| Fe-1 |
0.00083 |
0.00071 |
| Fe-2 |
0.0036 |
0.0031 |
| Cd-1 |
0.0034 |
0.0035 |
| Cd-2 |
0.0048 |
0.0045 |
| Cd-3 |
0.0063 |
0.0070 |
| Cd-4 |
0.012 |
0.013 |
| S-1 |
0.11 |
0.096 |
| S-2 |
0.0014 |
0.0012 |
| S-3 |
0.011 |
0.011 |
| ZBK410 |
0.050 |
0.047 |
| ZBK417 |
0.029 |
0.028 |
3.結(jié) 論
本文采用壓片制樣-單波長(zhǎng)激發(fā)能量色散X射線(xiàn)熒光光譜法測(cè)定含鐵物料中多種有害元素，利用基于基本參數(shù)法的無(wú)標(biāo)樣全譜擬合算法對(duì)目標(biāo)元素的基體效應(yīng)進(jìn)行校正并進(jìn)行檢測(cè)分析。通過(guò)正確度驗(yàn)證可知，方法滿(mǎn)足快速分析要求。
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