SMM published its September 11 sulphuric acid weekly review with the China copper smelting acid index at 1,418 yuan per tonne, down 121.5 yuan from the prior Friday print of 1,539.5 yuan.
The 7.9 percent weekly decline is the largest of the year in SMM's index, extending a ten-session run of weakness that included a 66.5 yuan single-day drop on Friday.
Regional price action centered on the Yangtze corridor. Daye Nonferrous in Hubei cut quotations by 85 yuan on September 5 and another 200 yuan on September 11, a cumulative 285 yuan reduction over two rounds.
Surrounding producers such as Tongling in Anhui followed Daye lower. Jiangxi smelting acid averaged 1,380 to 1,480 yuan, down 140 yuan week over week, while Anhui fertilizer-linked acid sat at 1,120 to 1,170 yuan on persistently low plant operating rates.
SMM said weak downstream demand fully offset supply-side reductions, including a large Henan smelter under maintenance since August 20 with cumulative acid impact near 50,000 tonnes.
In the same weekly account SMM flagged a domestic sulfur divergence from acid. Sulphur EXW Shandong on September 11 was quoted at 7,657 to 8,400 yuan per tonne with an average of 8,028.5 yuan.
That average is up 53.5 yuan from the prior Friday, a roughly 0.7 percent weekly gain and the second consecutive week of what SMM described as a V-shaped sulfur recovery.
SMM said upstream sulfur stabilized and rebounded but failed to transmit into acid pricing, indicating acid is driven by its own weak supply-demand balance rather than sulfur cost pass-through.
Asian export acid softened in parallel. SMM put FOB South Korea at 280 to 320 dollars per tonne averaging 310 dollars, down 10 dollars week over week, and FOB India at 300 to 350 dollars, down 15.5 dollars.
For North American recovered sulfur, the split matters because Chinese acid weakness can cap phosphate plant sulfur burn even when elemental sulfur spot rebounds domestically.
Shengyishe's September 10 national benchmark at 8,264.25 yuan and SunSirs port consolidation near 7,800 yuan granular sit in the same domestic sulfur recovery frame SMM mapped in Shandong.
QatarEnergy's September contract at 880 dollars FOB and theoretical CFR southern China above 1,070 dollars remain the seaborne reference for Pacific netback math on Alberta tonnes.
Desk read: September 11 separates elemental sulfur recovery from acid collapse. Watch whether Yangtze acid cuts deepen or whether sulfur's V-shape re-engages phosphate demand before Vancouver stem nominations firm.